PDA

View Full Version : Failure to Extract/Eject with PMC but fine with handloads?


Hoop
05-20-2011, 1:31 PM
I have a new build that won't extract/eject factory PMC bronze but is 100% with my handloads. They aren't getting stuck in the chamber, what is happening is the extractor just doesn't seem to be grabbing them (no abnormal case growth/cases don't have scratches or marks on them). The handloads that ran fine were 24.3 varget + 75bthp and 26 varget + 52hp.

Tried cleaning/oiling, swapped mags, pmc bronze ammo ran great in my other rifle so it has to be okay.

Any thoughts? I was thinking undergassed or weak ejector but then my handloads should burp too but it didn't, in fact it shot them excellently.

FeuerFrei
05-20-2011, 1:58 PM
Try shooting one round cycled from mag. One round only.
Will it lock back w/PMC?
Hand loads may be generating more pressure than PMC.
PMC is usually GTG in most ARs but I have seen otherwise.
Possible gas leak or smallish gas port hole in barrel.

Hoop
05-20-2011, 2:02 PM
I tried that at the range, it locked back fine with PMC. It will feed a new round from the magazine without ejecting the old casing. If anything it seems that the extractor is letting go too early w/factory ammunition.

FeuerFrei
05-20-2011, 2:13 PM
Extractor/spring/insert.
New complete bolt assembly or old recycled unit from another build?
Disassembled and cleaned before used?
Easy to swap with a "known good" bolt and test again.
If the swap works then the problem is in front of you.

Hoop
05-20-2011, 3:43 PM
Extractor/spring/insert.
New complete bolt assembly or old recycled unit from another build?
Disassembled and cleaned before used?
Easy to swap with a "known good" bolt and test again.
If the swap works then the problem is in front of you.

New bolt, and yeah swapping it with a known good one is what I'll do next.

krushed
05-21-2011, 3:05 PM
I had a CMMG midlength with the same problem with PMC and Remington .223, FTEs every few rounds. The solution was a dring extractor/insert upgrade from BCM for the bolt. After that it ran 100%.

Hoop
05-22-2011, 4:51 PM
Yeap, swapped bolts and it ran 100% but now it bends the case mouth on every other piece of brass. So I guess I need a heavier buffer or spring.

818gtiguy
05-22-2011, 7:06 PM
Is this a carbine, mid, or a rifle gas system? If a carbine, I would go with a H2 buffer. If a mid length, I would use a H buffer. I would also suggest a chrome silicone buffer spring from Sprinco. Tell me this, is the chamber and bore chrome lined? Also, did you see if your reloads were getting the case mouth bent too?

Hoop
05-22-2011, 8:18 PM
Most of the reloads didn't. It's a mid gas and I'm using a rifle buffer+spring.

818gtiguy
05-22-2011, 9:04 PM
Most of the reloads didn't. It's a mid gas and I'm using a rifle buffer+spring.

Hmmmmmm. If you are using a rifle buffer and spring, you can't go any heavier. The H and H2 buffers only apply on the carbine buffers. I'm thinking you have a rough or tight chamber. Or the gas port is too large(over gassed). Who is the manufacture of the bbl? .223 or 5.56 chamber? Also, does it have a chrome lined chamber and bore? I'm thinking more towards the tight/rough chamber because your reloads are hotter than the PMC, and there for would have more pressure to extract the spent cartridge. Where as the PMC is not as hot , and is not enough pressure to overcome the tightness of the brass in the chamber...

Hoop
05-23-2011, 7:02 AM
It's not a tight chamber, I think it's a combination of the gas port being a bit off, extractor too weak and just plain new rifle that needs to be shot. I'll just put some velcro on the forward assist (what the brass is hitting during ejection) and shoot it.