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Discussion Starter · #1 ·
So I finished building up an ACR pistol and checked its headspace and saw that it closes on the no-go gauge with little-to-moderate force on the charging handle. I was shocked to see this and relieved that I had 5.56 gauges on hand before I actually chambered a live round.
Upon seeing this, I was wondering if it's possible if the fitment of the barrel on the QD trunnion might affect the headspace? Inserting and removing the barrel into the QD trunnion took a lot of force and the torque lever isn't completely on the 6 o'clock.
For reference, the parts list on my ACR pistol are as follows:
  • Ballistic Advantage 11.3 Hanson Barrel (Brand new)
  • Used OEM ACR Bolt (Was told this was a low round count ACR bolt)
  • Reciever and Trunnion made inHuntsville, AL (S/N is 500+)
I thought maybe the bolt is the culprit but what is the possibility that the QD trunnion might be the cause because of it being too tight and not allowing the barrel to sit further in .

I would appreciate any help! Thank you in advance!
 

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I think the lock rings/washers are used for timing the locking position of the lock handle, but the headspace is another issue.

I think you'll need a factory barrel to ensure that the factory trunnion is the issue.

-OR-
You can switch to the non-QD trunnion system from Templar Precision. Since you're dealing with an ACR pistol, I don't think you'll be swtiching that often unless you see a 300blk barrel in your future.
 

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I think the lock rings/washers are used for timing the locking position of the lock handle, but the headspace is another issue.

I think you'll need a factory barrel to ensure that the factory trunnion is the issue.

-OR-
You can switch to the non-QD trunnion system from Templar Precision. Since you're dealing with an ACR pistol, I don't think you'll be swtiching that often unless you see a 300blk barrel in your future.
100% correct, I just went and looked at the position of the lock ring washer on my spare barrel and it has no effect on headspace....had the position switched in my head!
 

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Discussion Starter · #5 ·
Thank you all for the replies!
Upon further inspection, I’ve come to the conclusion that it might actually be the bolt after inspecting another ACR bolt that I know works.
First off, the “questionable” bolt has a lot of wear and has “dimples” on the rear of the lugs? Not sure if that’s normal to have structurally speaking…
Bumper Gun accessory Gas Metal Auto part

The bolt I know works just looks like a normal AR15 style bolt with no dimples and less wear on it…
Bumper Automotive exhaust Automotive exterior Auto part Trigger

Don’t really think there’s a fix to a bolt that fails a no-go gauge other than replacing it but that’s not really an option for me financially at the moment. So for the mean time, I’d like to be proven wrong if there’s a cheaper way, if at all, to fix a bolt’s headspace
Thanks again!
 

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Discussion Starter · #6 ·
Upon even further inspection, I’m more confused than I was when I started.
The bolt in question may be okay since it passes in my other ACR’s barrel assemblies. I finally took the barrel out and it seems to fail on the certain bolt but not my original bolt.
I guess now the real culprit is the barrel itself?
Honestly debating if I should just sent this in to be checked at. There’s too many variables that I may be missing here that may be beyond just an “out of spec bolt”
 
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