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TESTED: The Repeatability of the AXMC and Era-Tac QD Mount

Shooting the AXMC with Tangent Theta Scope and Era-Tac Mount

Quick detach everything has become a phenomenon within the shooting industry.  Quick Detach (QD) suppressors, scope mounts, bipods, barrels, lasers and lights.  I wonder what they’ll think of next.  Anyway—when it comes to QD items that affect the accuracy of the firearm, the biggest question is “is it repeatable?”  A valid question considering that is the entire point of these things, but that’s not always the case.  Absolute confidence is needed when utilizing a quick change system, so I grabbed Jason’s AX again and hit the range with a plan.

The multi-caliber Accuracy International AX that I reviewed in a previous article is a fantastic rifle. Paired with the Tangent Theta 5-25x56mm scope and a quick detach Era-Tac mount, I was confident that it would be fairly repeatable. Still, there’s only one way to find out. The procedure was fairly straight forward—I fired a cold bore at a separate target, then planted a 3 shot control group on the test paper.  I had already seen the accuracy potential of this rifle when it shot sub-quarter MOA a few weeks ago, but I needed to be sure to do it in the same conditions the rest of the groups would be at.  It was much warmer than the previous range session and the suppressor was changed from the Silencerco Hybrid, to the Silencerco Omega, which likely explains the .3 mil high impact relative to the zero with the Hybrid suppressor.  Once again, the control group was also sub-quarter MOA - so we had a great base for reference. From there, three other conditions were tested:

  1. Barrel off and on between shots on target two.
  2. Scope off and on between shots on target three.
  3. Scope AND barrel off and on between shots on four.

There was a 15 minute cool down between these conditions.  All were single fed, shot prone using an LRA F Class Bipod, Tab Gear Rear Bag and with factory Hornady 147gr ELD Match ammunition.  The side screw that tightens and releases the barrel was set to the AI spec 49 in/lbs using a torque wrench with a 4mm Allen tip.

For the first condition, I fired a shot then took off the barrel.  The barrel was a bit tight so with a soft rag protecting the finish on the barrel, I used the Silencerco suppressor tool on the flat spot on the barrel to encourage it off.  While it wasn’t a perfect fit, it worked.  Much to the amusement of the other people at the range—I did this twice. The three shot group produced a .49 moa group. 

Tangent Theta Scope with ERA-TAC Quick Detach Mount

The second condition involved removing the scope and reinstalling between shots. The Era-Tac QD is the best design I have ever seen. The very solid mount strength and the hook shape of the QD arms makes it easy to remove without breaking your fingernail off like some mounts. With a notation of where it was on the rail, I shot another group with the off-on cycle between. The group started well, but I sailed a round high and right, ruining what may have been a sub-half moa group. Actual measurement was .9 moa for those three shots. Final condition leads me to believe that this is a shooter induced flier, or possibly a mirage/wind condition that caught me.       

The third condition was the big one.  For those wanting to pack their rifle in a small bag or case, this one matters the most since the barrel and scope were taken off and reinstalled between shots.  This was actually very confidence-boosting since the three shot group produced a near perfect triangle shaped group of .45 moa.

AMXC Repeatability Test Target

These tests proved fairly harsh on the equipment and shooter.  With so many potential sources for error, everything had to go right.  There was no room for error on the rifle, scope, mount, or my shooting.  Normally for precision shooting, you don’t want to move anything except cycling the bolt between shots to ensure your position doesn’t change, thus potentially throwing off the next shot.  With this, each shot was a freshly prepared position with about a 3 minute gap between shots while the barrel and mount were removed and reinstalled.  Adding that to the obvious swaps I did on the rifle proved to me that the QD systems on the barrel and the scope mount are good to go. 

AMXC Barrel and Scope Removed

Equipment List:

Rifle (before barrel swap): Accuracy International AX308 Black

Butt Spike: Black Butt Spike for AI AXMC

Optic: Tangent Theta 5-25x56 Gen2XR Riflescope

Bipod: Long Range Accuracy Light Tactical Bipod - Long Legs

Scope Mount:  ERA-TAC 34mm Adjustable Inclination Mount - 37mm/1.46"

Suppressor:  SilencerCo Omega Silencer

Comments (3) -

  • Todd

    5/29/2018 10:16:55 PM | Reply

    I would be more concerned where the center of the group moves than group size.  

  • Carsten

    10/2/2021 8:15:11 AM | Reply

    Does the 1.46" mount allow full inclination with a 56mm scope?
    It seems to be close.

    • Derek

      10/4/2021 9:04:56 AM | Reply

      Hi Carsten,

      For most 56mm scopes, we have observed that 40 moa is about the max for that version.  Sometimes 50 moa if the scope is short and no sun shade is used.  The 1.65 will allow full 70 moa of adjustment.  Thanks!


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