Just to go over this: DPMS receiver, 20" .308 barrel, rifle gas system, Superlative adjustable gas block, I bit the bullet, found a H4 buffer for a decent price and it's paired with a extra extra heavy buffer spring. I took it out early in the week, and with the gas block venting at just shy of its complete capacity I got 22 rounds with no problem, then it started stovepiping. With the empties ejecting at 3 o'clock.
Thinks I, 'Maybe it's when it gets dirty that it starts it again', so when back home cleaned it thoroughly and lubed, then today took it to the range to try again.
Thinks I, 'Maybe it's when it gets dirty that it starts it again', so when back home cleaned it thoroughly and lubed, then today took it to the range to try again.
Nope. Same problem from the start.
So I'm out of ideas. Other than finding a open-minded priest.
Added:
Had a standard gas block when all this started.
Had a standard gas block when all this started.
I did get a new extractor/spring set, as a bunch of people mentioned that as a possibility.
Ejector is the same, but has been checked on function.
Works great bare, but add the backpressure of a can and this happens, with all indications being overgassed.
I have built several AR15s in the past, none of them had such a problem.
I have built several AR15s in the past, none of them had such a problem.
Blarg, dammit.
2nd Added:
Obviously there's something about adding the can on that's triggering this. Annoying as hell.
Obviously there's something about adding the can on that's triggering this. Annoying as hell.
And to Anonymous, somebody mentioned the gas port itself possibly being the problem, and it's on the list to check soon as I have time.
Again, folks, thank you for the comments, personal 'This happened', and other information
7 comments:
I'm sure you must have changed the gas tube, yes? Is it possible that there is a small imperfection on the bolt, receiver, some where inside the damn thing that is "sometimes" inducing just enough drag on the bolt to slow it just enough to drop the recoil impulse below what's needed to retrack the bolt enough to eject the empty? Got a little long winded there, sorry
Consider this not advice, but rather an observation:
I've no gunsmith or armoror, but I have assembled somewhere around 10 AR style rifles in 5.56mm including an A2 style "old" National match rifle and an M4 style "new" NRA match rifle capable of sub MOA accuracy. I've Assembled an AR-308 and two ARs in 6.8spc...one with a 16" barrel and one SBR.
The only rifle of all those I've ever had issues with short stroking and stovepiping is the one with an adjustable gas block.
Take that as you will.
Tight chamber, enough so that extraction becomes sticky when it heats up? Maybe try some reloads that have been sized with a small base die?
Sounds like your barrel is overgassed quite a bit. If that's out of whack, what else is wrong with it?
new extractor and new ejector spring?
I ran into a similar situation a couple of years ago: extraction and ejection were borderline on a Rock River 308. The rifle came with a 16" barrel, and it worked perfect as such. I wanted to find that extra 50 feet per second for longer range shooting, so I replaced the 16" barrel with a Rock River 20" barrel, and rifle length gas system. I called Rock River before I did this, and asked one of the techs for advice, then followed the advice they gave. The result was the same as what you're describing happening to you. After much head scratching and attempted troubleshooting, a friend mentioned "Have you measured the gas hole in the new barrel?" I had not, but I ended up using a bit and reamer to open the gas hole to match the old barrel (I actually made it a little wider). My extraction/ejection problem disappeared. I installed the original non-adjustable gas block back, and it has been running flawlessly since then. Just my experience.
"...I got 22 rounds with no problem, then it started stovepiping". Something has got to be changing or moving.
"Works great bare, but add the backpressure of a can and this happens,..." So, can goes away, problem goes away. Maybe that's where the problem is?
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