AR scratching brass in mag

[BUGUDY]

Problem is such; after cycling a round, the next round to be cycled in the mag is getting scraped. A full length scratch. I assume the bolt or carrier is the culprit, but I don't see the remedy. I have 2 PMags and a mil spec mag, happens with all three.
Doublestar upper w/appx 500 rds
CMMG lower
Here is a picture of what they look like.

 

[rcmodel]

GI aluminum mags sometimes leave a scratch from the feed lips, but P-Mags seem unlikely.

I think it is probably a bur or sharp edge on one of the locking lug cuts in the barrel extension.

Feel around in there with a Q-Tip and see if anything snags cotton fibers.
Also look for brass tracks rubbed off on anything sharp.

If you can find it, polish the edge off slightly.

rc

 

[BUGUDY]

RC. I drop the mag after one cycled round, the top round will have a nice scratch while stll in the mag. The scratch round has never left the mag, but if I keep cycling, every round will get the mark. It has to the bolt or carrier, but I cannot fing a burr on either. Also there is no adjustment?

 

[matrem]

Humor me.. & RE check for a burr on your bolt lugs.

 

[BUGUDY]

No burrs on bolt lugs.I used a magnifying lens this time. Normal looking wear.

Edit: Upon further investigating, it is only one lug on the bolt causing the scratch, so it is every other round getting scratched. On the left side of mag pointing downrange. I don't get it, yet.

 

[Jim K]

Try this: With the bolt locked back, insert a loaded magazine. Let the bolt close but do not fire. Remove the magazine and see if the top round is scratched. If it is, you know the scratch is caused by the bolt going forward. If not, reinsert the magazine and retract the bolt; again remove and inspect the top round. If there is now a scratch, you know it is from the bolt moving backward.

That doesn't solve the problem, but it lets you know where to look for brass marks and sharp places on bolt/bolt carrier.

Jim

 

[BUGUDY]

Jim, That is exactly what I did last night and found that it did scratch every other round on the left hand side of mag, when cycling forward. So for some reason the one particular lug on the bolt is causing the problem

 

[BBBBill]

Is the magwell possibly broached a little off center (slightly to the right)? What brand is the gun?

 

[BUGUDY]

It is a Doublestar rifle kit.. The problem just started or at least got worse so that I noticed it.

Edit; For the record it turned out to be the carrier. With more light and magnifying glass, and slowly cycling rifle, I could see that the bolt never touches the next to chambered round. Hence it had to be the carrier. I used a fine tooth file on the left front leading edge, which looked fine, and rounded it a bit. Fixed.