Hello All,
Well, I was trying to conduct some research into the 6.8 and compare it to 5.56 for speed and shootability in standard drills for possible military application. So, I ordered one of Noveske's new barrels in 6.8. It has the Mod 1 chamber, which is their version of the SPC II and is 14.5" Originaly I built it up on an LMT upper reciever with LMT carrier and an older gas tube. Bolt is a CMT/STAG 6.8 bolt since Noveske accidently sent me a 5.56 bolt with the barrel.
The problem: I get intermittent short-stroking. Here is what I have done.
Magazines: 2 PRI, 2 Barret, 3 Cproducts. Load one and shoot to check for bolt lock. I might fire 5-10 before it will do it, but it does it in all magazines.
I have used two differnt bolts, both CMT/STAG, two upper recievers, BCM and LMT, 3 gas tubes, two Colt cam pins, lots of lube -SLIP2000 EWL. I have pulled the barrel off and checked the gas block and gas port for obstuctions. Nothing and no sign of excessive gas leaking out. Gas port measures .070 with a caliper. I've tried two different lowers and three weights of buffers, H, H2 and H3. Action spring is new colt in one, LMT in the other lower. Still does it.
Ammuntion: Reloads - SSA small primer brass, new and once fired. 110gr Hornady OTM, Light crimp with LFCD, 30.1gr H322 over a Rem 7.5 primer. Avg Velocity is 2638 for 15 shots on an 80 degree day. SD12.4, ES 47
I've done the standard checks. No unussual wear marks in either reciver where the cam pin might be rubbing. Gas keys are tight and properly staked. Lube is generous. Chamber is clean and dry. Normally I would think this was an ammo issue, but that velocity should be more than good enough to cycle the action reliably. So, hopefully I didn't miss anything.
Anyone care to comment on what might be the problem? I'm really at a loss on this one and I'm pretty familiar with AR's.
My next step is to run all shots over the chrony to see what the veloicty was when it short strokes.. Round count right now is about 300 down the bore. After that I'll have to suck it up and try some factory ammo. I was hoping to run this for one day in an upcoming Pat Rogers carbine course, but it looks like it won't be ready. Any thoughts are appreciated. Thanks
Tom
