So I’ve just finished putting together a LR308 build and here is what I have that is pertinent.
JD Machine upper/lower
18.5" Criterion barrel from Fulton Armory
NiB BCG from Harris Tactical (made by WMD I believe)
Lubed up with fireclean
I haven’t shot any rounds through it yet. With nothing chambered I can cycle the bolt open and closed no problem, smooth as can be. I picked up some A-Zoom snap caps and tried running those through just to see how it cycled. After releasing the bolt I could not pull the charging handle back with one hand. Tossed the gun up on my cleaning station and if I pull back on the charging handle with both hands I can get it to pop free. I repeated 5 or 6 times with the snap caps, same result. I read around and found where some people questioned the specs on the snap caps. I then tried factory ammo and had the same results there. I can always get the bolt unjammed but it takes a significant amount of force.
I was worried that maybe my chamber was out of spec. I removed the upper and I can drop a round in no problem and it falls right out?
What do y’all think? Is this just a case of tight tolerances and I need to go ahead and run some rounds through it or do you think it is not safe to fire? Do I need a different bolt? Never had this problem so I’m not sure where to go from here. Any help would be much appreciated.
If I look up the mag well with the bolt closed, no round, I can see the position of the bolt based on the ejector pin. If I then load one of the snap caps, the bolt jams closed, and then I remove the mag, I can see the bolt is not fully rotated to the position that is with no round by looking at where the ejector pin is. That would leave me to believe the bolt is not fully locking?
So it if fails with the go gauge and doesn’t fully rotate, how do I move forward to fix it?
Back when I was 308 bolt shopping, I saw some reports of those NiB 308 BCG’s having incorrect headspace. They were apparently made by 7.62 Industries but marketed under other brand names as well. They were the only 308 BCG’s that I have seen that were NiB coated.
I would measure bolt depth and see if you can find someone to loan you a known good 308 BCG for comparison. My bet is that it is NOT the Criterion barrel though. If the bolt depth is short, you could either have your existing bolt machined deeper (may not be possible based on metallurgy) or get a different bolt.
Thanks for the heads up on the 7.62 Industries bcgs. After some reading, it looks like there is pretty good chance that is my issue. Going to round up another bolt and confirm.
No problems out of my 762 Industries NIB BCG. Over 250 rounds so far without a problem. Purchased my Criterion barrel from Fulton Armory and sent them my bolt to headspace as well.
Could be headspace but I’ve had this happen on a new 308 build and all it needed was more lube… Lube the hell out of the bcg…tolerances can be tight on a fresh build.
I also had problems with “failure to chamber” on a 308 AR that I had. Turned out it was the ammo - I had reloaded some brass that I pulled bullets from verify powder charge. Turns out they were incorrectly sized by the person I got the original ammo from. After running them through a FL sizing die with the decapper removed, they chambered/fired fine. Of course this is not likely your issue.
All of the 308 AR’s that I have put together were “tight” in the beginning, but chambered/ran just fine. If it won’t close on factory ammo, something is wrong.
Did you measure the depth of the bolt face recess? That is the first step…