SBR failures to feed

[MistWolf]

Circle 10, did you perform a lock back check? Without doing a lock back check, you can only guess whether or not your AR is short stroking.

If it is short stroking, do not assume it's under gassed. Your gas system could be leaking or partially blocked.

If you're ejection seems erratic, take a close look at the extractor spring.

I doubt the crushed case is from your AR. Cases are crushed like that from a stovepipe.

A lighter buffer will not fix short stroking. At best, it can only mask the problem until whatever is causing the short stroking gets worse.

[Circle_10]

I started to write a response earlier this morning, but got sidetracked, are the fail-to-feeds all on the right side of the mag?

That would tend to point me at the right feed ramp. The right ramp in the picture seems a little proud, but really not that bad.

Carbine buffer, known good spring and see how it shoots. Use various mags. If you are still having the same problems, I'd see about smoothing the feed ramp.

ETA - Just a thought - are you sure the gas tube is entering the carrier key smoothly? I could see where that might slow things down a bit - wouldn't necessarily impact ejection, but might feeding.

Yeah, all the FTFs were on the right side. I probably wouldn't have looked twice at that right feedramp otherwise. I have shot this exclusively with GI 20s and 30s so far (the FTFs were only with 30s, but that might just be coincidence) but next time around before doing anything else I may try Pmags because they basically cover the feedramp extension in the upper receiver anyway. Although I want the gun to work with GIs too, it might be informative to see if I have any issues with Pmags.

I don't think the interaction of the gas key and gas tube is the issue, as the FTFs are all like the one pictured, where the BCG is stopping well before the key reaches the gas tube.

Circle 10, did you perform a lock back check? Without doing a lock back check, you can only guess whether or not your AR is short stroking.

If it is short stroking, do not assume it's under gassed. Your gas system could be leaking or partially blocked.

If you're ejection seems erratic, take a close look at the extractor spring.

I doubt the crushed case is from your AR. Cases are crushed like that from a stovepipe.

A lighter buffer will not fix short stroking. At best, it can only mask the problem until whatever is causing the short stroking gets worse.

I didn't do the "load one round in the mag, fire, repeat.." lock-back check but I didn't have any failures to lock open at the end of firing the last round in any of the mags.
Ejection seems fairly consistent, mostly about 3 o'clock from what I can tell.
I'm kind of leaning toward the crushed case being from someone else at this point. Just odd that it's the same headstamp (not that 2018 Lake City is rare ammo or something) and was sitting on top of the ice with the rest of my brass.

One thing about the gas system being blocked...I will note that in order to get a preliminary zero with the gun, I had to dial the windage farther to the right than I normally like, not *all* the way, but the aperture is pretty noticeably over to the right. I considered that the FSB might be slightly canted but with the high winds both days I figured I'd need to try to re-zero on a calm day to really be sure what was up with that.
If the FSB is canted though, could that be causing a partial obstruction of the gas port, or would the FSB really need to be *way* off to cause that issue? (because like I said, the rear aperture is off to the right, but not actually maxed out yet)

[ViniVidivici]

The hole on the underside of the FSB is so much larger than the gas port, I can't imagine a slight cant choking off any gas.

I'm thinking if it were canted that far, it'd be WAY over, probably wouldn't even be able to zero.

[Circle_10]

The hole on the underside of the FSB is so much larger than the gas port, I can't imagine a slight cant choking off any gas.

I'm thinking if it were canted that far, it'd be WAY over, probably wouldn't even be able to zero.

That's kinda what I figured but I thought it was worth mentioning just in the off chance that there was in fact a connection.

I'm strongly suspicious of the right-side feedramp at the moment.

So, if the rounds are indeed failing to feed due to that slightly "off" section of the right feedramp, could the reason that the rounds can't overcome that slight imperfection in the ramp be because of a gassing issue (Either legit undergassed, leaking, or obstructed somewhere)? Or could that minor of an imperfection in the feedramp cause issues on its own in a properly gassed gun?

The ejection pattern seems healthy but my understanding is that ejection trajectory can be symptomatic of a gassing problem but is not, by itself, diagnostic of one. So presumably "proper" ejection doesn't always mean proper gassing.

[1168]

I’ve had failures to feed that were because of barrel feedramps standing slightly proud of the receiver M4 cuts, so I would personally be looking at that.

[Circle_10]

I’ve had failures to feed that were because of barrel feedramps standing slightly proud of the receiver M4 cuts, so I would personally be looking at that.

If worse comes to worse I can pull the upper apart and see how that barrel mates up to the ramps in some other receivers too I suppose.

[Iraqgunz]

One reason why we polish feedramps and check their interface with the feed cuts in the upper. Get a Dremel and some Cratex and polish both sides first. I think this will solve your issue.

https://www.brownells.com/gunsmith-t...turer_1=CRATEX

[Circle_10]

One reason why we polish feedramps and check their interface with the feed cuts in the upper. Get a Dremel and some Cratex and polish both sides first. I think this will solve your issue.

https://www.brownells.com/gunsmith-t...turer_1=CRATEX

Thanks! I can do most work on my ARs myself, but anything involving a Dremel may be something I let a professional handle just to be safe. I do appreciate the info though.

[Circle_10]

Is it possible there's some other issue besides just the ramp, and the FTFs are just a symptom? Because technically, on semi automatic, even with GI mags, shouldn't the cartridges not be feeding at a low enough angle to even catch that "lip" between the barrel extension and receiver cut in the first place?
Is that where an H2 buffer might come into play?

[1168]

Is it possible there's some other issue besides just the ramp, and the FTFs are just a symptom? Because technically, on semi automatic, even with GI mags, shouldn't the cartridges not be feeding at a low enough angle to even catch that "lip" between the barrel extension and receiver cut in the first place?
Is that where an H2 buffer might come into play?

That’s what I’ve always thought, until I had the points snag the extension when dropping the bolt on a fresh full aluminum 20 rnd mag.