Marlin Model 9 Camp Carbine Fired Brass Question

[Sidewinder]

I have a question about burn marks on the side of my fired brass. These burn marks are pretty extensive, going about half way up the side of the case. It appears to be doing it in the same clock position as each round is fired. This is factory loads and not hand loads. The burn marks are more prominent on Winchester White Box 9mm Luger from Wal -Mart than it is on Federal 9mm Luger factory ammo from WM.

The Marlin Camp 9 is a "blow back" action, almost identical to the Ruger 10/22. At the recommendation of many Camp 9 owners on the forums, I replaced the recoil spring (11 lbs) with a 16.5 pound spring, I'm considering replacing that spring with a 21 pound spring.

I'm interested in comments about why this is happening. None of the shell casings are split, but burned pretty bad. I thought that possibly there was a chamber irregularity, but the Federal brass is not burned as bad. Any Smiths with an opinion? Thanks.

Edited August 27, 2010 by Sidewinder
Punctuation

[roverboy]

Some brands of ammo will sometimes leave burn marks on the cases. Its possible the brass isn't expanding against the chamber wall. This will a lot of times leave burn marks. I've handloaded for over 20 years and see this with light loaded .38's. I wouldn't worry much about it. Somebody else on here may have something else.

[Dolomite_supafly]

It is nothing to worry about. My wife's 9mm AR does the same thing with most ammo. As long as you aren't getting a face full of gases I wouldn't worry about changing anything. If you are then, as you said, you might want to go heavier on the spring.

Dolomite