Sooty brass in surplus rifles

[MAKster]

I have a m96 Swedish Mauser. I've noticed that the entire length of the brass cases are sooty after firing. I just noticed it last time I went to the range but cannot recall if it was always like this since I hadn't shot the rifle in a long time. Is dirty brass common? I assume this is because the chamber is loose. When I bought the rifle I had the headspace checked and the gunsmith said the bolt closed on the no-go gauge, but not on the field gauge which is fairly common on surplus rifles. I've only fired about 150 rounds since then. The brass doesn't appear to be stretched, but I'm concerned about the headspace. Any idea how many rounds it would take for a rifle that previously passed the field test to become unsafe?

 

[Vaarok]

Commercial ammo is generally loaded light. Remington and I believe Winchester ammo further uses an undersized case-head. Both of these factors can result in an improper seal.

Lug setback is variable depending on pressure and wear, but it would probably take in the neighborhood of three to five thousand rounds to influence headspacing, and the wear would be more from working of the bolt than recoil and pressure.

 

[rcmodel]

+1

Low pressure ammo is not expanding the case enough for a good seal.

Excess headspace manifests itself in cracked cases or case head separations, not sooty cases.

rc