My bolt carrier jams after 3 rounds. have shot appox. 2000 rounds. b4 this. have cleaned every thing- what else can i do?

Is the bolt locked into the lugs or is bcg stuck rearward?

Explain what your "bolt carrier jam" looks like.

I've fired lots of 5.56 and never seen a jammed bolt
carrier.

Are there any aluminum mags involved, that have been
dropped, fully loaded, on hard stand, landing on their
feed lips, per chance?

After firing, spent ejects and next cartridge jams as the bolt carrier goes forward. Feels like there isn't enough gas pressure to push the round forward fast enough.

Shooting only brass 223, new pmags also, bolt carrier seems slow going forward after round ejects. Did swap out carrier and bolt in Colt AR 15 with same result.

When you say you swapped out the BCG, did you put the M&P BCG in a Colt upper and the symptom followed the bolt, or did you put the Colt BCG in the M&P upper and the symptom stayed with the M&P upper?

Gas pressure only runs the bolt back. The buffer spring drives the bolt back forward.

From what I understand of what you are describing and the chamber and locking lugs in the barrel extension look good, it could be a recoil spring problem.

This description isn't gas-related. Where is the live round which is stripped from the magazine?

Have you broken the weapon down and looked at the buffer / spring?

Thank you - will remove recoil spring.

Will look at buffer/spring- thank you.

Could be gas related... sounds like he is describing a short stroking situation. Enough gas to push the bolt back far enough to eject, but isn't compressing the spring to get a good push forward.

Moving the upper to another lower would tell us... if the symptom follows the upper, it could be a gas issue. Could be magazine related as well... not enough info from the OP to diagnose.

OP, try with multiple mags. Does it occur with all mags, or only one? If all mags, put your M&P upper on a known good lower. Does the symptom follow the upper?

Sounds like a cleaning issue to me.

In every semi-auto I've seen that had this "slow action" feeling, the problem was alleviated with a good cleaning. The BCG on an AR does get dirty very easily. So, start there. Do a field strip, clean and lube. Then try again.

__________________
Freedom isn't free.

When troubleshooting any AR, always start with a lock back check.

First, insert an empty magazine and verify the bolt will lock back when manually cycling the action.

Next, load one round in the magazine, insert the mag in the rifle and fire the round. If the bolt locks back, the AR is not short stroking.

and with this Gentlemen, we have the Smith and Wesson forum, "post of the day"!

What kind of ammo are you shooting? I've had similar problems with Independence

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