I just swapped barrels out to a new 16" M4 profile.

I used the original bolt which had about 3k rounds on it.

I had the HS checked and started breaking it in.

I sighted it in and have about 300 rounds through the new barrel so far.

Functioning has been 100%.

I tore it all down tonight and when I removed the extractor from the bolt I noticed fine brass "dust" inside the FP channel and around the extractor channel.

I have never seen this before.   It would appear as if the extractor is shaving some brass off of the round as it chambers or extracts.   I did notice a sharp edge (very small) on 1 side of the claw of the extractor I hadn't noticed before.   I took a fine stone and smoothed off the offending edge.

Is it normal, with barrel swaps, to have the forced exerted on the bolt change because of the new barrel lugs on the barrel extension ever so slightly??

Would this potential change in lockup forces cause issues such as this with the extractor??

None of my ARs or M16s ever did that, but I had an HK SL8 that did it. Never had any problems with it though.

The new edge that seemed to form is on one side of the extractor, at the front,  where it bears against the side of the channel cut into the bolt the extractor rides in.

It's almost as if the extractor is being pushed harder to one side causing it to bear harder against the side of the channel in the bolt.

That's why I'm wondering if the new barrel, and barrel extension lugs, were exerting a new force on the bolt head causing this.

As I said, functioning has been 100% yet I'm concerned about brass shavings, even though they are VERY small, almost dust like, getting into the ejector and causing issues.

I'll shoot it more and see what happens I guess.

I may try a new extractor and see if that minimizes or eliminates the brass shaving issue I'm seeing.