Circle_10
05-13-17, 05:45
I was shooting my carbine, a retro build, off a rest the other day and was getting these same malfunctions over and over.
http://i.imgur.com/TnKq17C.jpg
http://i.imgur.com/Ppo0hPN.jpg
When I got the first one I briefly thought it was a regular double feed, however upon clearing it, it turned out the top casing each time was a spent one that failed to eject, with the lower round being a live cartridge trying to feed into the chamber.
One thing I noted was that it only happened with one specific Okay brand 20-rounder when I was firing it slowly off a rest. Cycled fine when fired offhand with a couple Okay 30s both slow-ish and as fast as I could. I also loaded up and fired the problem 20 rounder offhand without issue.
At home I checked the gas key, ejector, extractor and gas rings and all seemed fine.
Went back out with the carbine two days later and although the weather kept the firing session short I tried shooting off the rest with a few different mags and once again had the failures to eject with the same mag and no issues with the others. Most of the FTEs looked more or less identical to the ones the previous day, with a couple that were more like stovepipe malfs where the case head had made it out if the ejection port, but the neck was being held in by the bolt, with a live round trying to feed into the chamber as usual. This time the malfs only happened during the first half of the mag.
My first inclination would be to blame the mag however I didn't think failures to eject were generally attributable to bad mags. The mag was probably getting pressure exerted on it when I was shooting off the rest but I'd always heard that unless something is out of spec that shouldn't cause a malfunction. And even then I'd think it would be more of a straight-up failure to *feed*.
The best theory I could come up with so far is that the mag is ever so slightly out of spec, and generally not enough to cause an issue firing off hand, but the pressure exerted from shooting off the rest is pushing it up or causing it to shift just enough that the BCG is dragging on it when cycling.
Anyone have any better ideas? The gun is my first assembled-from-scratch AR so the notion that I might have something incorrectly during the process is nagging at me.
Gun specs as follows if it's relevant: Brownells A1 upper, 14.5" BCM barrel, carbine gas length, BCM bolt carrier group, currently on a placeholder Stag lower until I get a proper A1 style, the Colt receiver extension has an "H" buffer in it.
Ammo was from a batch of Prvi Partizan M193 with an '07 headstamp.
http://i.imgur.com/TnKq17C.jpg
http://i.imgur.com/Ppo0hPN.jpg
When I got the first one I briefly thought it was a regular double feed, however upon clearing it, it turned out the top casing each time was a spent one that failed to eject, with the lower round being a live cartridge trying to feed into the chamber.
One thing I noted was that it only happened with one specific Okay brand 20-rounder when I was firing it slowly off a rest. Cycled fine when fired offhand with a couple Okay 30s both slow-ish and as fast as I could. I also loaded up and fired the problem 20 rounder offhand without issue.
At home I checked the gas key, ejector, extractor and gas rings and all seemed fine.
Went back out with the carbine two days later and although the weather kept the firing session short I tried shooting off the rest with a few different mags and once again had the failures to eject with the same mag and no issues with the others. Most of the FTEs looked more or less identical to the ones the previous day, with a couple that were more like stovepipe malfs where the case head had made it out if the ejection port, but the neck was being held in by the bolt, with a live round trying to feed into the chamber as usual. This time the malfs only happened during the first half of the mag.
My first inclination would be to blame the mag however I didn't think failures to eject were generally attributable to bad mags. The mag was probably getting pressure exerted on it when I was shooting off the rest but I'd always heard that unless something is out of spec that shouldn't cause a malfunction. And even then I'd think it would be more of a straight-up failure to *feed*.
The best theory I could come up with so far is that the mag is ever so slightly out of spec, and generally not enough to cause an issue firing off hand, but the pressure exerted from shooting off the rest is pushing it up or causing it to shift just enough that the BCG is dragging on it when cycling.
Anyone have any better ideas? The gun is my first assembled-from-scratch AR so the notion that I might have something incorrectly during the process is nagging at me.
Gun specs as follows if it's relevant: Brownells A1 upper, 14.5" BCM barrel, carbine gas length, BCM bolt carrier group, currently on a placeholder Stag lower until I get a proper A1 style, the Colt receiver extension has an "H" buffer in it.
Ammo was from a batch of Prvi Partizan M193 with an '07 headstamp.