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Noveske Barreled upper - Short Stroking

3407 Views 22 Replies 12 Participants Last post by  tpe187
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

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Thanks, I'll check out the standard carbine buffer. I did size my brass before loading the first time, but I'll check out those dimensions you listed. Most of the rounds fired were from the initial batch of 300 new cases so that is one possible cause. I'll get back to you guys on the results.
Sorry, I knew I forgot to add some things.

Yes, two bolts - CMT/STAG and two different carriers - LMT and BCM. Both are properly staked and known to work in my other AR's

I'm using Forester dies for the reloads. I have been thinking about the small base dies as recommended here and I'll order a set, just to be sure.

I'll check the trigger, but I think its a standard LMT in the one rifle and a standard Colt in the other.
The ejection pattern is good. Cases eject at between 3 and 4 o'clock about four feet away. Cases aren't dinged either.

The malfunction is an empty chamber when firing a string of 5 to 10 rounds. This occurs off the bench when using the mag as a monpod as well as when running drills with nothing touching the magazine.

The carrier also fails to lock back periodically when testing mags with one round for lock back.

I checked my brass and that seems to be ok. Neck od is within spec. Cases manually extract without effort.
I cleaned the chamber and could not see any imperfections.
I blackened a cartridge and hand chambered it. Upon extraction there were no marks on the body, neck or bullet.
When chambering from a magazine I do get one long striation from the base to the shoulder. I figure thats from the feed ramp.

I will try the standard carbine buffer and one other lower before I go to differnt ammo. Kind of a bummer right now.

As to my research, I'm working on a masters degree and I could pick a decent topic. Basically, my thesis is that our small arms equpment, doctrine and training are not adequate for operations in Afghanistan where engagements occur beyond the 300 meters most units train to. 5.56 fragmentation is limited to under 200 meters from an M4 and M249 which further compounds the problem. Our SDM doctrine sucks in that it specifies some fairly basic instruction but does not standardize a rifle for his use. I've seen M4's with ACOG's up to M14's with 3.5x10 power Leupolds.

As part of my discussion I talk the merits of the 6.8 vs others like 6.5 Grendel, heavy 5.56 like MK262, or 7x46mm ARC. To compare the effect of higher recoil from 6.8 I've run some standard drills to get a baseline time for 5.56 and compare. I would hardly call the results conclusive, but I consider the 6.8 extremely managable and worth the reduced capacity and extra weight.
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Bushmand - don't worry about it, after all I've covered I have almost run out of options. Yes, I had another shooter, An NRA Highmaster Service Rifle and long range shooter. He had the same problems, and I didn't say anything to him until he mentioned it closed on an empty chamber.

I think I might have it figured out. As per the recommendation to check the gas tube pin location, I checked it with other tubes and it was the same. The gas block lines up directly over the gas port and is pinned to the barrel. What I did find is that the pin location in the gas block is slightly off. Not anyting like a total obstruction but maybe 1/6 the lenth of the tube opening past perfect alignment. I'll see if I can snap a picture for you. I have a Larue gas block that I'll try out and see if it works. If it does, I'll either leave it alone or sent the Noveske barrel and block back to have a new block with the correct pin location installed. Thanks for all the help. I might have an answer tomorrow. Fingers crossed.

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Its a carbine length gas system. I hope to get to the range tomorrow or sunday and test the different gas block with the standard carbine buffer. I'll let you guys know.
sorry I wasn't clear. The gas block and barrel ports are aligned correctly. The gas tube pin hole in the gas block appeared to be in the wrong location. My basis for this was that when installed and off the gun I could look into the hole and see part of the tube as if it wasn't lined up correctly. That was my reference for 1/6 of the hole diameter being off. Hard to visualize by that explanation. When I looked at it again, it was just that the hole in the Noveske block was larger than the hole in the gas tube. When viewed from the other side, it appeared as if an equal amount of tube was present on either side. The larue gas block I had as a reference is a smaller hole and matches the diameter of the gas tube hole.

So, after all that, I changed the gas block to the Larue, changed the buffer to a standard carbine and used a completely different lower with standard hammer. Had been using a Geiselle trigger. While not conclusive, I did not have any malfunctions today, but I only had a chance to fire 50rds out of the PRI mags. I've got a Pat Rogers class this week and I don't intend on using the 6.8 upper for one of the training days, as I had originally. When I get back I'll try to run about 300 rds through it to make sure its good. Thanks for all the very detailed thoughts on my problem.

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