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AXTS Weapons Systems A-DAC-F Lower Receiver

8/25/11 - The A-DAC-F Lower Receiver from AXTS Weapons is the first and only AR-15 lower to incorporate a mechanism that activates the bolt catch with the magazine release button, allowing right-handers to clear remedial action malfunctions without removing the firing hand from the pistol grip. It's also the first to have multi-configuration safety markings specifically designed to accommodate the Battle Arms Development short throw safety.



Back in December of 2009, I was contacted by Josh at then-unknown AXTS Weapons about a right hand bolt catch idea for the AR-15, wondering if I was interested in taking a look and providing some thoughts/input. This started more than a year of email and phone discussions with Josh, about both the design and function of the A-DAC lower, and a separate fully-ambidextrous billet lower design that became the AX556. Josh also consulted others in the shooting industry and sport, and after a year and a half, the A-DAC-F is finally here. The A-DAC-F is a forged AR-15 lower receiver with the A-DAC feature.

A-DAC Concept - As a left hander, when I want to lock the bolt carrier back on an AR-15, I use my trigger finger to depress the bottom of the bolt catch while pulling back the charging handle, and locking the carrier to the rear. In order to perform that task on a standard lower, a right hander usually has to break his firing grip on the weapon, and use his right hand to pull back the charging handle while using his left to depress the bottom of the bolt catch. The idea behind the A-DAC is to provide ambidextrous control of the bolt catch, allowing the right-handed shooter to lock back the bolt carrier without having to break his firing grip on the rifle. This allows the rifle to be controlled better and reduce the time taken to clear the malfunction. The standard method of pressing the bolt catch on the left hand side can also be used.

When would the A-DAC be used? For the administrative task of locking the bolt to the rear without a magazine in the rifle, or more importantly, for remedial action malfunction clearing when immediate action (Tap, Rack Bang) fails to clear the malfunction. Remedial action is required when dealing with malfunctions like a double feed, bolt override, or charging handle impingement. This involves both clearing and unloading the weapon, which means that the magazine is removed and the bolt carrier locked back if possible (not possible with the charging handle impingement). The A-DAC enables the user to perform the dual function of dropping the magazine (or allowing it to be ripped out of the magazine well if stuck), and engaging the bolt release catch to lock the carrier back with the right hand, and without breaking the firing hand grip from the weapon. This effectively eliminates some of the steps that the right-handed user needs to go through to lock the bolt back, saving time.

A-DAC Description - The A-DAC-F (Ambidextrous Dual Action Catch, Forged) Lower incorporates the mechanism that AXTS refers to as the Dual Action Catch. This consists of a new custom bolt catch, magazine release button and custom designed Mag catch spring, the A-DAC pin, and the modified lower. The parts come with the lower. The A-DAC pin is the only additional part added (when compared to a standard receiver), and is completely internal to the receiver. The nice thing about having this feature integral to the lower is that there are no add-on external levers needed. The magazine release button has two angled flats (so it doesn't matter which orientation it's installed in the receiver); one of which will push against the A-DAC pin.

The A-DAC-F receiver has a hole connecting the magazine release button channel and the bolt catch channel, drilled at an angle. The A-DAC pin rides in the hole, and contacts the back of the magazine release button, and the bottom of the bolt catch. When the magazine release button is depressed, and moves from right to left, it pushes the pin up and at an angle, which pushes the bottom of the bolt catch up. The AXTS website has a series of illustrations which show exactly how this works here. The A-DAC pin can easily be removed if desired, and the magazine button will function as 'normal' without lifting up the bolt catch.


A-DAC button components

A-DAC pin in receiver hole

When the A-DAC concept was first shown and discussed on forums, there were some questions/misconceptions about its function. Hopefully I can help clear up things up a bit. Also listed are some of the A-DAC-F's features:

  • The A-DAC is not a bolt drop device - pressing the magazine button pushes up on the bolt catch, engaging the front of the bolt carrier when it is in the rearward position. It does not drop/release the bolt. Dropping the bolt is accomplished the standard way by pressing on the top of the bolt catch.
  • "I don't want to drop the magazine every time I need to lock the bolt back" - The A-DAC doesn't preclude you from locking the bolt back the standard way by pressing the bottom of the bolt catch. Pressing the bottom of the bolt catch does not affect the magazine button and will not drop the mag. Again, if you don't want to drop the magazine when you lock the bolt back, just use the bolt catch.
  • Will pressing on the bottom of the bolt catch to lock the bolt back drop the magazine? - No. It'll function as normal. The bolt catch doesn't 'pull' on the A-DAC pin.
  • Will ambi mag releases actuate the A-DAC mechanism? - No, an ambi mag release button on the left side will not actuate the A-DAC mechanism. The A-DAC functions only when the right side mag release button is pushed inwards. The Norgon ambi-catch works by the lever pivoting on the mag release shaft, and does not move the magazine release button on the right side. So, it doesn't affect the A-DAC whatsoever. The Troy ambi mag catch pulls the entire assembly to the left, and moves the right side button inwards, but not enough to actuate the A-DAC pin.
  • Can I remove the A-DAC pin? - Yes, very easily. It's removed by pulling the magazine release assembly all the way to the left, like when you unscrew the magazine catch to remove it. Removing it returns the lower to 'standard' functioning, and pressing the mag button will not actuate the bolt catch.
  • Can I convert an existing lower to have the A-DAC feature and just buy the A-DAC parts? - Quick answer: no. Long answer: It's always possible to drill the A-DAC pin hole in a standard lower, but you'd just have to do it properly (precise angle/location/diameter/surface finish) or it won't function.
  • Multi-configuration safety markings - The A-DAC-F lower is designed to be used with any standard safety, or the BAD-ASS-ST 45-degree short throw safety from Battle Arms Development. The BAD-ASS-ST has a small pin on the axis of the safety to prevent it from being installed in receivers with standard Safe-Semi markings. This is to avoid confusion about what position the safety levers are in. The A-DAC-F lower also has the relief slot so that the BAD-ASS-ST axis can be installed without modification. The A-DAC-F lower has two pictograms - one of a bullet with a line through it indicating 'safe', and another bullet indicating 'fire'. Below the 'fire' symbol is an arc which covers 45° to 90°, indicating that the rifle is on 'Fire' when the lever points anywhere in that region. It works safeties with either 45° or 90° throws.
  • Tensioning screw - A small set screw with a plastic tip is pushes up against the bottom of the rear takedown pin lug on the upper receiver, taking out any play. It's located behind the pistol grip screw hole and adjusted before the pistol grip is installed. Note that different uppers will have slight differences between the rear takedown pin lug height, and the set screw might be looser or tighter on different uppers. Upper-lower play has no effect on mechanical accuracy, but some folks would rather have no movement between the two. It need not be used if you don't want this feature.
  • Large magwell chamfer - the inside of the magwell has an enlarged chamfer to facilitate inserting magazines.
  • Traction grooves at the front of the magazine well - I don't use a mag well hold, but these can help improve purchase when controlling the rifle by holding it at the magwell (transitions to pistol, transitions from one shoulder to another etc).
  • Materials - The A-DAC-F lower is machined from a Mil-Spec 7075 T6 forging, and anodized per MIL-A-8625F.

Left side

Right side

Top

Bottom



Enlarged mag well chamfer

The BAD-ASS-ST is shown below, partially installed (in the left photo), illustrating how the pin passes through the slot. The next three photos show the lever in the safe, 45° and 90° positions. The BAD-ASS-ST only goes to 45°; the standard one would be at 90°. There are no selector stops on the left side of the receiver - they're carefully machined off to eliminate the stop being in the way with the thin BAD lever, and also to provide the room to lay out the dual selector markings. As you can see in the photos on the right, the standard receiver selector stop blocks part of the thin BAD lever, making actuation with the right thumb less positive. With the A-DAC-F receiver, the lever is unimpeded.


BAD-ASS-ST pin

Safe

45°

90°

Standard receiver with thin BAD lever

ADAC-F with thin BAD lever

Assembly and Observations - Assembly of the A-DAC-F lower went without a hitch. I installed a McCormick trigger module in it (hence the non-standard trigger pins with the C-ring), and a Troy ambi magazine release (which I prefer over the Norgon). I've been having good performance with the Vltor A5 Buffer and Recoil System, so I also installed that on the A-DAC-F. It's shown below with the Addax Tactical ATAC GPU, so I've installed the FRS A5-length anti-tilt buffer in it. I also installed the Wilson Combat trigger guard, just to try something different than the Magpul. Feels similar, looks fine. FDE Cerakoted BAD-ASS short levers provide additional visual confirmation of what position the safety lever is in.

After assembling the A-DAC-F lower, I proceeded to fit check it with various uppers, and all of them fit fine, including the Vltor MUR which tends to fit tight on some lowers. There's little to no play in the uppers I installed, and use of the tensioning screw wasn't necessary. All magazines I tried with the A-DAC-F lower dropped free - USGI, TD ARC mags, later model Pmags, Lancer, HK. Cosmetically, I like the simplicity of the markings - the pictograms and the simple geometric AXTS logo.


Vltor A5 buffer tube installed




With Addax ATAC GPU



I think that the A-DAC-F feature is most beneficial to right-handers. As a lefty, locking back the bolt on an AR-15 has always been easy to do, just by reaching up with the left index finger and depressing the bottom of the bolt catch without breaking the firing hand grip. I'm not a righty, so my double-feed malfunction clearing using my right hand feels awkward and clumsy. However, going through the drill and breaking the movements down into discrete steps makes it apparent to me that being able to lock the bolt back using the right side magazine button, then removing the magazine without having to move your firing hand is quicker than the 'standard' way. For those who don't like change, you don't ever have to use the A-DAC feature if you don't want to. I'll wager that most folks won't ever discover the A-DAC feature unless they're told and shown it, as the A-DAC-F lower operates like a standard lower, if you use it as such.

The benefit of having an integrated feature in the lower, vs. a bolt-on device are obvious:

  • Nothing to snag on clothes or gear
  • Nothing to accidentally trip the bolt release when reloading
  • Nothing inside the trigger guard that could be snagged with a gloved hand
  • No interference with the Norgon Ambi-catch or Redi-Mag
  • No weight added to bolt catch that can sometimes cause it to not lock open on the last round
  • Adds only one additional part to the rifle (internally) - none externally
  • No screws to come loose
  • Compatible with all upper receivers
  • Can be field stripped without tools

I demonstated the A-DAC-F to some fellow shooters at the range during a carbine class, first asking them 'show me how you lock the bolt back when clearing malfunctions'. They showed me, each time breaking their firing grip on the weapon. I then showed them using the A-DAC and that's when their eyes got wide. As they tried it out, you could literally see the light bulbs going on in their heads.

The price of the A-DAC-F is very competitive when compared to other forged lowers (especially when you get a discount when ordering the lower and selector together directly from AXTS), and for the extra features I think it's worth the small difference. You only have to use it a couple of times to realize the benefits of the A-DAC feature.





 


 

AXTS Weapons Systems AX556 Lower Receiver

10/16/11 - As a left-handed shooter, I've been waiting for something like the AX556 Lower Receiver from AXTS Weapons for a long time. It's the first fully ambidextrous lower receiver for the AR-15 platform and every function on the lower receiver is now accessible from both sides of the weapon. The added ambi controls have been integrated into the lower with the minimum number of additional parts, while maintaining the standard location and functionality of the legacy controls.

Back in December of 2009, I was contacted by Josh from then-unknown AXTS Weapons about a right hand bolt catch idea for the AR-15; wondering if I was interested in taking a look and providing some thoughts/input. This started more than a year of email and phone discussions with Josh, about both the design and function of the A-DAC feature which is incorporated into their A-DAC-F Forged lower, and the fully-ambidextrous billet lower design that became the AX556 pre-production and final models shown here. Josh also consulted others in the shooting industry and sport, and after a year and a half, the AX556 has finally been introduced.

While AXTS Weapons may be a relative newcomer in the AR-15 industry, they're no stranger to manufacturing, as AXTS is a subsidiary of X Factor Machine & Design, Inc., much like Vltor is part of Abrams Airborne Manufacturing. AXTS performs all their design and machine work in-house.

Ambidextrous controls; to add or not to add? - Adding ambidextrous controls to an AR-15 always seems to be a hotly debated subject. I'm not sure why people are so opposed to adding ambi controls on the AR15 when they wouldn't blink at someone adding an ambi safety to a .45 ACP. For what I've observed, the people who argue against the idea are right handers, or left-handers who have not tried ambidextrous parts. Two most commonly used arguments against ambi controls are "I've never had a problem using the standard controls" and "If you rely on ambi controls then you'll screw up when you pick up a standard AR. You should keep all controls standard". My answer to the first statement is "If you're happy with what you've got, there's no reason to change."

As for the second statement, I can see where that has merit for someone who is on a tactical team in LE or the military, where some sort of standardization amongst team members' weapons might be desirable. But for a civilian, I don't think that the argument holds as much water. I'm sure many will disagree with me, and that's fine, but it's my own sincere opinion. As a civilian, there is very little chance that I'll ever use an AR-15 in defense, and even less chance that it'll be with someone else's AR instead of my own. The only time I shoot someone else's rifle is at the range, and if I forget for a second that I'm using a standard lower and screw up, the most I'll suffer is a little embarassment. Ambi controls allow me (as a lefty) to operate the AR as efficiently as a right-handed person does. I have no reason not to set up my weapons to work as efficiently for me as possible, 99% of the time, for the 1% chance that I'll suddenly forgot how to operate a standard AR when my life is in danger. Who's to say that I'll actually be picking up an AR instead of an AK or HK, with completely different controls?

The AR was designed with right-handed controls as standard. But that was 50 years ago, and times have changed. As far as keeping controls 'standard', I believe that the new standard for the AR should be with ambi controls. But that's just my opinion as a left-handed nobody, and I realize that my opinion doesn't carry much weight (if any at all). However, when Knight's Armament Company (KAC) introduced the KAC SR-15 IWS (Integral Weapons System), which incorporated the final redesign and innovations of legendary firearms designer Eugene Stoner's (the original designer of the AR) it featured ambi controls. The KAC SR-15 IWS (Integral Weapons System) has an ambi safety, ambi bolt release, ambi magazine release and ambi sling mounts on the lower receiver. If Gene Stoner and KAC saw the value in adding ambi controls to his original design, maybe it's time for a change.

A fully ambi receiver will benefit left and right-handed shooters alike, by allowing either to shoot and manipulate the weapon controls from either side. As weak/support-side training becomes more common, it's my belief that the advantage of ambi controls will become more evident.

One of the reasons that AXTS started the development of the A-DAC feature and the fully ambidextrous receiver was in response to changes to the M4 proposed by the U.S. Army to Congress in 2009. This included adding ambidextrous controls to the receiver. Over the past 18 months, both the A-DAC-F and pre-production AX556 receiver have been involved in military testing (3 independent tests of the A-DAC-F and 2 independent tests of the AX556), with zero failures related to the AXTS receivers. At the time of this writing, there continues to be significant military interest in both receivers.

A-DAC Concept - While the AX556 is not the first lower featuring ambidextrous controls, it does so to the fullest extent, and is the first truly FULL ambi lower receiver for the AR platform. Ambi safeties, bolt drops and magazine releases have been available as drop-in parts for standard lowers. However, an integrated ambi bolt catch that can both lock the bolt back and release it has been more elusive. The aforementioned KAC SR-15 IWS does have an ambi bolt release, as do billet lowers like the POF-USA and Mega (to name a couple), but none have an ambi bolt catch that enables a right hander to LOCK the bolt BACK without breaking the firing grip. The disadvantage to adding external bolt-on devices vs. integrated ones is that they're not always compatible with other ambi controls, and can be more subject to damage/breakage.

As a left hander, when I want to lock the bolt carrier back on an AR-15, I use my trigger finger to depress the bottom of the bolt catch while pulling back the charging handle, and locking the carrier to the rear. In order to perform that task on a standard lower, a right hander usually has to break his firing grip on the weapon, and use his right hand to pull back the charging handle while using his left to depress the bottom of the bolt catch. The idea behind the A-DAC is to provide ambidextrous control of the bolt catch, allowing the right-handed shooter to lock back the bolt carrier without having to break his firing grip on the rifle. This allows the rifle to be controlled better and reduce the time taken to clear the malfunction.

When would this be used? For the administrative task of locking the bolt to the rear without a magazine in the rifle, or more importantly, for remedial action malfunction clearing when immediate action (Tap, Rack Bang) fails to clear the malfunction. Remedial action is required when dealing with malfunctions like a double feed, bolt override, charging handle impingement etc. This involves both clearing and unloading the weapon, which means that the magazine is removed and the bolt carrier locked back if possible (not possible with the charging handle impingement). The A-DAC enables the right-handed user to perform the dual function of dropping the magazine with the right side magazine button (or allowing it to be ripped out of the magazine well if stuck), and engaging the bolt catch to lock the carrier back with the right hand, all without breaking the firing hand grip from the weapon.

A-DAC Feature Description - The AX556 receiver utilizes the same basic design as the A-DAC-F (Ambidextrous Dual Action Catch, Forged) Lower, and incorporates the mechanism that AXTS refers to as the Dual Action Catch into the receiver. This A-DAC system consists of a custom bolt catch, magazine release button, and the A-DAC pin. The A-DAC pin is the only additional part added (when compared to a standard receiver), and is completely internal to the receiver. The nice thing about having this feature integral to the lower is that there are no add-on external levers needed.

Like the A-DAC-F, the AX556 receiver has a precisely machined hole connecting the magazine release button channel and the bolt catch channel at an angle. The A-DAC pin rides in the hole, and contacts an angled face on the back side of the magazine release button, and a recess in the bottom of the bolt catch. When the magazine release button is depressed, and moves from right to left, it pushes the pin up the angled hole, which pushes on the bottom of the bolt catch rotating it upward. The AXTS website has a series of illustrations which show exactly how this works here on the A-DAC-F. The function is the same on the AX556. The A-DAC pin can easily be removed if desired, and the magazine button will function as 'normal' without lifting up the bolt catch.

For more details on the A-DAC feature and function, please read my A-DAC-F writeup.

AX556 Features:

  • Fully ambidextrous controls - All functions can be accessed from either side of the receiver: magazine release, bolt catch, bolt drop, safeties. All the controls are protected on the receiver by raised 'fences' to prevent inadvertent actuation.
  • Accepts all standard pattern AR15 magazines - pressing the magazine button pushes up on the bolt catch, engaging the front of the bolt carrier when it is in the rearward position. It does not drop/release the bolt. Dropping the bolt is accomplished the standard way by pressing the upper bolt catch paddle on the left side or by pressing the bolt drop lever on the right side.
  • Marked 'CAL MULTI' - Although the AX556 is primarily designed for the 5.56 NATO round, the receiver is marked 'CAL MULTI' to allow the user the option of building rifles in any vareity of different calibers, or swapping out uppers from one caliber to another.
  • Package includes the stripped AX556 lower and the following custom machined parts (all will be available for purchase as spare parts):
    1. Front takedown pin
    2. A-DAC pin
    3. Bolt drop pin
    4. Bolt drop plunger
    5. Bolt drop lever
    6. AXTS EBC (Extended Bolt Catch)
    7. AXTS ARHP - Anti-rotation hammer pin (you can also use a standard pin if desired)
    8. Magazine catch
    9. Left hand magazine release lever
    10. 3 custom springs
    11. Fulcrum pin (pre-installed) - this is the left hand magazine release fulcrum pin and is permanently pressed into place.
    12. AXTS SART (Self Adjusting Receiver Tensioner) -plunger, spring and retention screw
    13. Rear takedown detent retention screw with allen wrench
    14. Bolt catch pivot screw
    15. Bolt drop pivot screw
    16. 2 ball end allen wrenches for the small screws
    17. Magazine release button

     

  • Multi-configuration safety markings - The AX556 lower is designed to be used with any standard safety, the BAD-ASS 90-degree or the BAD-ASS-ST 45-degree short throw safety from Battle Arms Development. Personally, I prefer the short-throw 45-degree BAD-ASS-ST (shown in this writeup), which has a small pin on the axis of the safety to prevent it from being installed in receivers with standard Safe-Semi markings. This is to avoid confusion about what position the safety levers are in. The AX556 lower has the relief slot so that the BAD-ASS-ST axis can be installed without modification. The selector lever markings on the AX556 lower consists of two pictograms - one of a bullet with a line through it indicating 'safe', and another open bullet indicating 'fire'.
    On the A-DAC-F lower I reviewed above, below the 'fire' symbol is an arc which covers 45° to 90°, indicating that the rifle is on 'Fire' when the lever points anywhere in that region (for use with short throw and standard levers). This particular AX556 lower does not have the arc, as I requested that it just be marked for the 45° ST lever - the standard production one has the multi-configuration marking.
    There are no selector stops on the left side of the receiver - it was designed without them to eliminate the stop being in the way of the thin BAD lever, and also to provide the room to lay out the dual selector markings.
  • Flared magwell, large magwell chamfer - The magwell is flared and the inside of the magwell has an enlarged chamfer to facilitate inserting magazines.
  • Traction grooves at the front of the magazine well - I don't use a mag well hold, but these can help improve purchase when controlling the rifle by holding it at the magwell (transitions to pistol, transitions from one shoulder to another etc). The machined cutouts on the sides of the magazine well also add to the security when gripping it there. It's not compatible with Redi-mags.
  • Built-in spring-loaded plunger for upper/lower tension - On the final production model (scroll down below), a spring loaded plunger instead of a tension screw pushes up on the rear takedown lug of the upper.
  • Captured takedown pin detent spring - The takedown pin detent hole is tapped on the end, and a small set screw keeps the detent spring from flying out when changing receiver end plates and removing buffer tubes.
  • Materials - The AX556 lower is machined from 1.75" thick 7075-T651 billet aluminum on a high-speed 5-axis machining center. The AX556 receiver with all its function and form details requires 60 tools to complete on the machine. After machining and inspection on a CMM, the lowers are bead blasted, then Type III hard anodized per MIL-A-8625F. The AX556 weighs 10.5 oz while a stripped aluminum receiver weighs about 8-9 oz.

Pre-Production Model

The following are my observations on the pre-production model which I used for a few months, prior to the production model being released.


Left

Right

Top

Bottom



With Pmag

Ambidextrous Functions/Controls - Description

Bolt catch - As mentioned above, the AX556 receiver incorporates the A-DAC mechanism, which allows the right-handed user to lock the bolt back by pressing the right side magazine release button; without having to change the position of the firing hand. The AXTS EBC (Extended Bolt Catch) on the left side has an extended paddle at the top, which extends further back, enabling the left-handed shooter to drop the bolt more easily than the standard paddle. You get a bit more surface area and leverage, and don't have to reach as far forward. The bottom of the paddle has a slightly enlarged grooved pad that also makes it easier to depress with the left index finger to lock the bolt back. Right handers can slap the top of the paddle with the butt of the hand or thumb like normal to drop the bolt.

Bolt drop lever - The bolt drop lever is located on the right side of the receiver, just above the right side magazine button. Instead of the normal method of slapping the left side paddle with the support hand to drop the bolt, the right hander can use his index finger to drop the bolt from the locked-back position to chamber a round by depressing the grooved button. The button can also be used by left handers to drop the bolt by pressing the button with the thumb, right after seating the magazine; a method I find quicker than using my fingers on the left side to drop the bolt when reloading.

Magazine release - Except for the built-in A-DAC function of the magazine button, the right side button functions exactly the same as normal. The right hander presses the mag button on the right side to drop a mag. On the left side of the receiver, the magazine release lever pad is located below and behind the bottom of the bolt catch. It's slightly further back than a Norgon ambi-catch is, and slightly forward of the KAC ambi mag release (which I find is too far back). I have short fingers, so having it further back a bit means that I don't have to reach so far. People with larger hands can install a grip with a thicker backstrap if they find that they feel too cramped.

Safety/selector - While AX556 will accept any AR safety selector, the safety selector that AXTS recommends and sells as a discounted bundle package with the AX556 is the BAD-ASS from Battle Arms Development. In this case, it's the short throw 45° selector - the BAD-ASS-ST. The BAD-ASS is available in both standard 90° and short throw 45° configurations, with a myriad of different interchangeable levers (see my above writeups), making it the most modular and user-configurable selector lever system available thus far. As a lefty, it's one of the most important features (for me) to have besides the mag release.

All the various buttons are protected on the receiver by raised fences to prevent inadvertent actuation.


Bolt catch top view

Left side

Anti-rotation hammer pin

BAD-ASS-ST

Safe

Fire

Assembly and Observations - Assembly of the AX556 requires no roll pins and is pretty easy to assemble. If you've assembled an AR-15 lower before, you should have no problems installing the parts in the AX556. All the machined, proprietary parts will also be available as spares. On this particular receiver, I installed the Vltor A5 Buffer and Recoil System, along with a Geissele SD3G (Super Dynamic 3 Gun) trigger. The AHRP (Anti Rotation Hammer Pin) is fully compatible with all hammers that use standard pins, and a standard hammer pin can also be used in the AX556 lower. The AHRP is prevented from rotating by a small 'foot' at one end, that fits into a corresponding hole in the right side of the receiver.

The AX556 has a look typical of most billet lower receivers - angular and more 'faceted', rather than having the softer transitions of a forged lower. Some like the billet look, some don't. I like it, just as I like the angular shape of the Vltor MUR upper receiver and VIS. While I like the angular look of billet lowers, I'd like to see a 'smoothed out' version with more rounded edges and as much material taken off as possible. I hope to see forged lowers in this configuration in the future. The cutout pattern on the magazine well duplicates that of the Magpul Pmag; which I think looks pretty cool. While I'd rather have a pattern that is more 'neutral' and doesn't match any particular magazine, I can see the value of having additional traction in that area. Not to use for shooting with my support hand on the mag well, but when grabbing the rifle at the mag well when it's at my side (after doing a transition from rifle to handgun) and bringing it back up, or when switching shoulders. The quality of the machining is excellent.


SD3G trigger

Vltor A5 buffer tube installed


Vltor IMOD stock

The integrated trigger guard is curved for use with gloves. This is one area where I felt could be improved; I found the edges a bit sharp under some circumstances. I also found this true of some other billet lowers. I've been spoiled by rounded, smooth trigger guards like the Magpul, Oberland Arms or Wilson, so this is speaking relative to those, not the standard sharp edged trigger guard. Anyway, the AX556 trigger guard can use more of a bevel or some rounding out. It's not noticeable when shooting; only when performing certain actions where the weight of the rifle is borne by the firing hand, and the edge of the trigger guard rests on the middle finger. Installing the TangoDown BG-16 pistol grip required a tiny bit of alteration to the tang (duckbill) of the grip, that bridges the normal gap on a standard receiver. I had to dremel it a bit to accommodate the downward-sloping bottom of the AX556 trigger guard. The AXTS logo is machined on the bottom of the guard. The AX556 is shown below with a KAC upper, with the Armament Dynamics ACLM ambi charging handle, which to me, is an important component to complete the full ambi package.


KAC URX upper



Using the Ambi controls - Here are some of the observations I came up with, when using the ambi controls on the AX556. Although I'm a lefty, I also tested them out as well as I could as a righty. You have a number of options - find the way that feels more natural to you.

Bolt catch - While the AXTS EBC (Extended Bolt Catch) on the left side has an extended paddle at the top, which extends further back, it's still a bit of a reach for me with my short fingers. As with standard lowers and bolt catches, I don't reach up with my index finger to drop the bolt, as the angle is too awkward. I relax my grip around the pistol grip, make a 'knife hand', and drop the bolt that way. With the extended bolt catch, I do find that I get a bit more surface area and leverage which does help. As for locking the bolt back, I've always found it convenient as a lefty since the bottom of the bolt catch is within reach of my index finger and easy to engage. Note that I'm using an Armament Dynamics ACLM ambi charging handle in the photo below. On the AXTS EBC, I'd like to see a bit of a scallop or step right above the bottom pad, to separate the pad from the rest of the lever. With gloves, it doesn't give the same tactile feel as the nubbin on the standard catch.


Locking bolt back with left index finger on bottom pad of bolt catch (L handed)

Dropping bolt with AXTS EBC (L handed)

Dropping bolt with EBC (R handed)

Bolt drop lever - The bolt drop lever on the right side of the receiver, enables the right hander to drop the bolt from the locked-back position to chamber a round by depressing the grooved button. It's further back on the receiver than the AXTS EBC on the left side, so it's not as much of a reach for my index finger. However, I still find the 'knife hand' feels much more natural. When new, the button was a bit stiff, but smoothed out with use (and a bit of oil on the bolt catch/receiver). What I find the right hand bolt drop lever most useful for, as a lefty, is for dropping the bolt by pressing the button with the thumb, right after seating the magazine. I found this method quicker and more positive than using my fingers on the left side to drop the bolt with the AXTS EBC after reloading.


Dropping bolt with right index finger (R handed)

Dropping bolt with 'knife hand' (R handed)

Dropping bolt with right thumb (L handed)

Magazine release/A-DAC button - Except for the built-in A-DAC function of the magazine button, the right side button functions exactly the same as normal. Using it as a right hander, I found it more convenient for locking the bolt back than using my support hand to actuate the bolt catch on the left side while I used my right hand to pull the charging handle to the rear. On the left side of the receiver, the magazine release lever pad is located below and behind the bottom of the bolt catch. I found its location quite natural to reach and had no issues dropping the mag. Like the bolt catch pad, I'd like to see some kind of step just forward of the pad, so I can feel it better. Right now, it's very flat, and I could use more tactile feedback when wearing gloves.


Left hand mag release (L hand)

Right hand mag release (R hand)

Locking bolt back using mag/A-DAC feature (R hand)

Safety/selector - What can I say? The BAD-ASS-ST (short throw) lever is my favourite set up. It's something I asked Battle Arms Development to make, and I'm glad that they did. The short, 45° arc is quick, doesn't get in the way as much as a standard length 90° lever, and is easy to flip on or off. All my lowers now have the ST levers installed.

Pre-production model feedback and desired changes - After spending some time with the AX556, I really liked the concept, but I felt that it still had some small changes needed, and that it wasn't yet ready to be released. I relayed the following feedback to Josh at AXTS, who had also compiled some feedback from other beta testers like Travis Haley, Jason Falla, Robb Jensen, Luis Gines, Team 144, Pat Goodale and Rob Tackett.

As mentioned above, I felt that AX556 can use a bit of tweaking with the controls (to provide more tactile feedback when wearing gloves), and that was relatively minor. For the receiver, the most important change necessary (in my opinion) was to make the trigger guard more comfortable. I asked Josh to incorporate a flat section (like an undercut), just forward of the pistol grip, and also to chamfer the edges of the trigger guard. I had also spoken with Jason Falla (RedBack One), who was another beta-tester, and he had voiced similar concerns, especially with the trigger guard. I shared the list of my suggested changes with him and he agreed on all points.

For the left side Bolt Catch I suggested adding a notch to separate the lower pad from the bar above it for better tactility. The finger can better sense a pad if it's separated from the rest of the lever with a raised or lowered portion. Josh also opened up the receiver fence in that area to accommodate larger fingers and gloves.

For the right side bolt drop lever Josh said he had gotten feedback from Travis Haley, Rob Jensen, Luis Gines, Pat Goodale, and Rob Tackett all agreeing that while the pre-production RH bolt drop was among the most ergonomic they had used; it could be made even better by making the paddle as large as possible. Travis Haley suggested making the paddle slightly longer for people with shorter fingers, to make the serrations a coarser pitch, and to make the serrations horizontal rather than vertical. The horizontal serrations to help prevent the finger from sliding down off it during actuation as the finger has more tendency to slip down instead of forward/aft, and the coarser pitch to provide a more positive grip. Along with these, Josh and I came up with a couple other improvements and ultimately we agreed that the following changes would make the right side bolt drop the best it could be in providing the most positive actuation - no matter whether the shooter was right or left handed, wearing gloves, or operating with sweaty hands:

  • Make the pad area as large as possible
  • Make the pad longer, towards the shooter's hand
  • Make it extend more towards the bottom of the receiver
  • Make the paddle stick out a bit further
  • Add a slight angle to the paddle

Since AXTS performs all their design and machine work in-house, Josh was able to make drawing changes quickly - sometimes the same day we discussed things. After discussing the details and exchanging numerous drawings, Josh agreed that the changes would make for a better product and decided to roll back the planned June release to incorporate the changes. So, I sent my pre-production model back for Josh to cut metal so I could test them out, and then he'd incorporate them into the final production model if all was well. The changes are shown below. Since this was just a test bed, the cuts were not refinished. As you can see, the trigger guard was recontoured (note that it's thin because material couldn't be added back), and made a world of difference. It's now the most comfortable guard I've felt. He also made the changes to the controls seen here.


Left side changes

Re-shaped trigger guard

Re-designed bolt drop (silver)

Bolt drop installed

Josh wanted to refine the trigger guard further, and came up with another variation - it's the top one in the 2nd photos below with the curves coming to a point at the back. I felt that it'd be better without the point, and sketched up the bottom design. Without really feeling it, it'd be difficult to determine which one was more comfortable, so Josh made up a couple of test pieces with both cuts, to see how they'd feel, and sent them to me. After going back and forth, the bottom one that I suggested had the slightly better feel, so that's what we went with. It's to this level of detail that Josh worked to, when making the changes. All this took time, which is why the initial release date was pushed back a few months. It was the right thing to do, and the final product is all the better for it.


Trigger guard test pieces

Two designs, top and bottom

Final choice


 

Final Production Model

The final production model incorporates all the changes to the pre-production model listed above, which are:

  1. Completely re-designed trigger guard with undercut and chamfer for higher grip and comfort. The engraved AXTS logo on the trigger guard was also moved to the forward section of the guard, rather than at the rear.
  2. Chamfer on back side of left side bolt catch for added clearance to upper receiver
  3. Notch added to bolt catch above bottom pad for increased tactility
  4. Larger shelf cutout around bottom pad of bolt catch for better access with gloved fingers
  5. Step added to left side magazine release catch in front of pad for increased tactility
  6. Right side bolt drop lever pad increased slightly in size, small angle added for ergonomics, and grooves changed to horizontal ones
  7. The lines-per-inch of the control pads has also been decreased for better traction (larger grooves)

Bolt catch changes

Production version

Note that my particular lower has dedicated 0-45° safety selector markings, as I only ever intended to use a 45° throw safety with it. The standard production AX556 has the multiple configuration markings, identical to the A-DAC-F in the picture shown here:

Shown below is the final production AX556 (except for the safety marking mentioned above). The opening of the AX556 mag well is about 25% larger (by area) than a standard mag, and flared with an enlarged chamfer to facilitate easier magazine insertion. All edges and corners have been machined with radiused edges at large end of the chamfer but even more importantly the inside edges where the angle transitions into the magwell itself. This in combination with the very large chamfer provides an almost guaranteed mag insertion even when the magazine is significantly mis-aligned on it's way up to the receiver as might happen in a high stress reloading. It's compatible with the SureFire 60 and 100 round magazines. The photos on the below right illustrate the difference between the AX556 well and a standard one.


Final production version right side





Mag well comparison


Two additional features were added to the final production version, which delayed the release by a couple of weeks. AXTS decided to delay the release a bit, with the new features, rather than implement them on the 2nd run. They didn't want their first customers to miss out, and I think that the short delay was definitely worth while:

  • AXTS SART - Self Adjusting Receiver Tensioner - Rather than a nylon tipped tension screw that's adjusted to eliminate the play between the upper and lower receiver, a spring loaded plunger pushes up on the rear takedown lug of the upper. The SART feature can be removed if desired by unscrewing the set screw at the bottom of the receiver, just at the rear of the grip lug. The plunger pushes up with just the right amount of tension - not so much that it's difficult to depress. While upper-lower play/slop doesn't affect accuracy, some folks like a more 'solid' feel between the two assemblies, and this provides it without needing any adjustment between different uppers.
  • Captured takedown pin detent spring - The takedown pin detent hole is tapped on the end, and a small 4-40 set screw keeps the detent spring from flying out when changing receiver end plates and removing buffer tubes. The rear takedown pin is installed, then the detent and spring. The set screw is installed behind the spring - I didn't trim my spring length; it worked just fine as-is.

Auto tension plunger

Plunger access

Captured detent spring

The new trigger guard is perfect, in my opinion. It blends just about perfectly with the Magpul MIAD grip as well as the extended tang on the TangoDown BG-16 (no alteration needed). The quality of the machine work that AXTS does is second to none.


Magpul MIAD





With Vltor MUR upper



Notes/Observations - At the range, the AX556 has become my favourite lower receiver, hands down. While I've had some ambi controls on other lowers, the AX556 is the first one that is truly ambidextrous. All functions can be performed with either the left or right hand. It's not mirrored from left to right, but the location of the controls are intuitive after just a short time. As I mentioned above, as a lefty, I actually found the right side bolt drop to be my preferred way of dropping the bolt on a full mag (with my right thumb after inserting a mag), rather than the left side bolt catch, as I don't have to shift my firing grip to drop the bolt. I posted a brief video illustrating it here. The addition of an ambi charging handle makes the rifle completely ambidextrous.

The changes to the final production model may seem individually minor (except for the trigger guard), but when taken together, I found the improvement significant. Kudos to AXTS for taking the time to make the changes. The AX556 is not the cheapest lower; it's in the ballpark of the other only ambi receiver, the KAC SR-15 E3 IWS (which commands a premium price). Even so, the E3 is not FULLY ambi, as a right hander cannot lock the bolt to the rear without moving the right hand unless a bolt-on device is used. When you add up all the different features that the AX556 offers, that you cannot get on any other lower receiver, it's a good value for the money. I'd rather have the AX556 than any other lower available, and I'm not sure I can think of anything else I'd want in a lower at this moment.











As with the forged A-DAC-F lower, the right handers who tried it get very excited when they use the A-DAC system of locking the bolt to the rear vs. the standard method. When clearing simulated double feeds or bolt over base malfunctions, locking the bolt back and ripping out the magazine (which usually doesn't drop free during these types of malfunctions) is just a simpler and quicker process than before for right handers, as the firing grip can be preserved. Also, as with the A-DAC-F, you don't have to use the A-DAC feature - you can always lock the bolt back the traditional way with the left side bolt catch. Using the new ambi controls doesn't take long to get used to, and you can always operate the AX556 controls exactly as you would a standard lower, and ignore the ambi controls if you choose. Better to have and not need than need and not have.

As a left-handed shooter in a right-handed world, I've noticed more and more guns with ambi features introduced over the years. As support-side shooting is taught more commonly now than it was 20 years ago, even right handers have begun to realize the advantages of having ambi controls on both handguns and rifles. I feel that fully ambi controls on weapons should be the rule, rather than the exception; and the AXTS AX556 sets the new standard for AR-15 lower receivers (in my humble opinion).

I can honestly say that I've been waiting for a receiver like this since 1986 - the year I got my first AR-15. That's 25 years at the time of this writing. All I can wonder is 'what took so long?'.


 

 

 

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