FTF, is this undergassed? .300BLK

[Tim K]

.300 BLK SBR running a 5" can. I've not seen this failure before. I can only guess it's undergassed. It looks to me like the bolt is not coming back far enough to get behind the case head.

Whaddya think?

http://i27.photobucket.com/albums/c173/tkulin/IMG_1884_zps7a0f4ebf.jpg (http://s27.photobucket.com/user/tkulin/media/IMG_1884_zps7a0f4ebf.jpg.html)

http://i27.photobucket.com/albums/c173/tkulin/IMG_1882_zpsebac2b6e.jpg (http://s27.photobucket.com/user/tkulin/media/IMG_1882_zpsebac2b6e.jpg.html)

[ray1970]

What kind of magazine were you running? I had a similar issue with the 20 round Pmags.

[DEAGLER]

Was it a 1 time thing? Occurrence rate?

[Tim K]

2 different 30 rounds mags. One a pmag, the other a steel mag.

Four failures in 40 rounds.

[KS63]

What ammo, gas system length, gas port size, buffer weight and recoil spring weight?

[Hoser]

Yup. Most likely undergassed.

Inside of gun looks dry. Add another bucket of oil.

[Tim K]

I thought so, too. It ran fine with the 9" can, but I'm guessing it was marginal. Going to the 5" can (and being dirty and under-lubed) was probably enough to get it to short stroke.

I'll lube the crap out of it. I'll also go up another drill size on the gas port.

[colorider]

I would do a few things 1st before drilling a bigger gas port.
see how it runs without the can
check your mags. I have had many malfunctions using older gen pmag 20s and some pmag30s. Gen 3 pmags of all sizes have been flawless.
Clean and lube.