450 bushmaster cycling issues

[FDchief8]

Looking for some insight……

Working on an AR 450 bushmaster. 16 inch generic barrel with carbine gas system. Standard gas block and buffer / buffer spring. Nothing fancy and not my build. Just trying to tune this dag blame thing for a friend!

When it cycles it throws the brass to about the 2:30 position indicating it is over gassed but it is only spitting the brass out about 18 inches from the receiver which makes it look like it’s under gassed. Rare occasion it will cycle correctly and load another. Most of the time the bolt catches the brass (not the case head) about middle of the case. Then it jams. I’m leaning towards undergassed but the 2:30 ejection has me baffled.

Sorry for throwing gas on the dumpster fire, I looked and couldn’t find any threads dealing with this. Has anyone ran into this sorta thing before?

 

[hlee]

Forget about the ejection angle. Start with it dribbling brass out, and/or short stroking. This sounds like under gassed.

What gas block? Is it adjustable?

If adjustable, is the gas block wide open? Have you confirmed that the gas block is aligned with the gas port in the barrel? Have you measured the gas port diameter?

It is possible that it is WAY overgassed, outrunning the mag spring, AND has weak ejection. But, that’s a lot to go wrong all at once. BCM sells an extractor spring upgrade that is relatively inexpensive, and this can resolve weak ejection (if the case is falling off of the bolt face before it is forcefully ejected.).

Those more knowledgable than me can give recs for gas port diameter.

 

[FDchief8]

Thanks for answering. It is a standard non adjustable gas block. And it seems to be aligned (99% certain). I was thinking it was under gassed also, but with such a heavy round, it just doesn’t math to me. I didn’t measure the diameter of the gas port in the barrel simply because I have absolutely no idea what it should be. Guess I need to measure that and double check alignment for the umpteenth time. I have seen several post about mag issues and they all recommend the lancer mag which I have several of, so I think I’m gonna try that also. Thanks again!

 

[hlee]

Thanks for answering. It is a standard non adjustable gas block. And it seems to be aligned (99% certain). I was thinking it was under gassed also, but with such a heavy round, it just doesn’t math to me. I didn’t measure the diameter of the gas port in the barrel simply because I have absolutely no idea what it should be. Guess I need to measure that and double check alignment for the umpteenth time. I have seen several post about mag issues and they all recommend the lancer mag which I have several of, so I think I’m gonna try that also. Thanks again!

I had a gun with anemic ejection. The kit linked below resolved it.

BCM® Extractor Spring Upgrade Kit

The BCM® Extractor Spring is a heavy coil design made for the increased extractor tension required on many AR15, M4, M16 short barreled rifles.

bravocompanyusa.com

5 bucks is a pretty cheap repair if it fixes the problem.

Could also be a function of bad geometry of the extractor claw.

Does the gun lock back on an empty mag? If it does, that mostly rules out under gassed. But, if it does not, or the bolt catch engages on the carrier nose instead of the bolt, it’s undergassed.