Gas/Jam?

[eldplanko]

Tried the search, but didn't quite find what I'm looking for…

I have a somewhat standard set-up I'm trying to diagnose a jam situation on…

Build: 11.5" barrel (BCM), carbine length gas system, low pro gas block, m16 bolt, mil spec buffer tube/spring, car buffer

Problem: Short stroke looking jams, with failure to ejects.

It seems like the rife is short stroking. When I load and fire a single round from the magazine, the bolt locks back.

Am I missing something else here, I though short stroke should not lock the bolt back.

[Inkslinger]

If it's locking on the last round, it's not short stroking. You should probably ditch the carbine buffer and use a H at a minimum. I use an H2 in my 11.5. If the cases are not ejecting, you may have something interfering with your ejector, maybe dirt or some brass shavings. What ammunition are you using?

[Servo]

If it's locking on the last round, it's not short stroking. You should probably ditch the carbine buffer and use a H at a minimum. I use an H2 in my 11.5. If the cases are not ejecting, you may have something interfering with your ejector, maybe dirt or some brass shavings. What ammunition are you using?

I Agree with this. Assuming some missing variables, it sounds like the rifle is trying to extract the round just a touch to early.

Some searching on common buffer weights for your barrel length, gas system and ammo should help figure out what buffer to go with. There is a fair amount of data on this site for 11.5s.

[MistWolf]

Your AR has an extraction issue. It may also have an issue with ejection. Over gassing does not cause extraction issues unless extraction is marginal to begin with. With the right spring and extractor, the rim will be torn off before the extractor will jump it.

The original extractor springs used in the M4 gave problems because the spring rate wasn't up to the job of the more violent extraction and wore out faster when compared to use in a rifle. As a stopgap, o-rings were used to beef up the spring rate. Colt developed a new spring, the copper colored spring, with a stiffer spring rate. It's supposed to be used without the donut.

When an AR starts developing extraction problems, it's not because it's over gassed (although it may in fact be over gassed), it's because either the spring is starting to sack, the extractor is wearing or both. Slowing down the carrier with a heavier buffer or by cutting down on the gas may allow the extractor to work reliably once more, but it's only postponing the inevitable. It's only a matter of time until the worn parts will need to be replaced

[eldplanko]

If it's locking on the last round, it's not short stroking. You should probably ditch the carbine buffer and use a H at a minimum. I use an H2 in my 11.5. If the cases are not ejecting, you may have something interfering with your ejector, maybe dirt or some brass shavings. What ammunition are you using?

Thanks for the insight. I took the bolt-carrier apart, gave the bolt and related parts a good cleaning; didn't see any nasties in the the extractor.

I've only tried wolf gold and ae 223 black box so far on this one.

[eldplanko]

I Agree with this. Assuming some missing variables, it sounds like the rifle is trying to extract the round just a touch to early.

Some searching on common buffer weights for your barrel length, gas system and ammo should help figure out what buffer to go with. There is a fair amount of data on this site for 11.5s.

Wish I had a super-slowmo camera...

[eldplanko]

Thanks for the insight. This is a new build; new parts. Bolt/carrier is a Rainier arms. I'm going to starts to try the parts swap with a functioning rifle… see if I can narrow it down. Bolt/carrier will be first on my list.

[eldplanko]

Thanks for the insight. I took the bolt-carrier apart, gave the bolt and related parts a good cleaning; didn't see any nasties in the the extractor.

I've only tried wolf gold and ae 223 black box so far on this one.

Oh yeah… single shot with these eject normally… does that make a difference?

[Ryno12]

Have you tried different ammo and mags?

[MistWolf]

My guess is your malfunction is an empty case and a fresh round jammed in the action. That's the extractor releasing the spent case before it can be ejected. That's an extractor problem