AR15 Troubleshooting (SBR)

[Lyonsgrid]

I bought this upper assembly from M&A parts in 2008. I had a few lowers SBR stamped around the same time. Last week I put this upper on a lower and had several failures to feed.

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I know the quality is not top notch. I just wanted to get some opinions on what’s going on and how to fix. Or should I just scrap the upper all together? I’ll add a quality upper when I can.

I was shooting Winchester ZZQ3315 62 gr Open Tip. I fired 50 rounds and had 6 failures to feed where the bullet was pushed way back into the case. Mags were (3) Colt GI 30’s. Failures happened with all mags. Not sure on the buffer, it has no markings and I don’t have a scale.

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Who wants to play internet gunsmith and help me out?

[SecondsCount]

Did you try different magazines?

Did the gun lock back on an empty magazine?

Edit to add... Your feedramp pics had not loaded the first time I looked. They don't look that great. Take a look at this thread for pics and details.

[Lyonsgrid]

I only ran the 3 GI mags and it did lock back.

[SecondsCount]

I only ran the 3 GI mags and it did lock back.

I edited my post. Check the feeding and see if the bullet is catching on the feedramps.

[HCM]

Concur on the feed ramps. The ramp cuts on the upper and the barrel extension don't appear to match up.That seems to be where the rounds are catching. You can see the brass marks on the left feed ramp and the brass shavings on you BCG.

Not sure is re-assembly or polishing / blending would help.

[StraitR]

Here is your problem.... looks like rifle feed ramps on barrel extension and M4 feed ramps cut in the upper.

Your feedramps...



ETA: Compare to "bad"...

[HCM]

Here is your problem.... looks like rifle feed ramps on barrel, and M4 feed ramp upper.

Good catch. That would be why they don't match up.