AR Sponsor
Posted: 10/1/2007 7:03:05 PM EDT
|
I have a 6920 and when I cleaned it, I discovered that there is a slightly pitted ring in the bolt face around where the primer would sit. There is also a pit about the size of a small grain of sand on the outside edge of the face. It is strange since the rifle has roughly 5K rounds through it with no issues and the ammo used was M855 GT (LC). I looked at the fired cases and there were not pressure signs and no signs of leakage. The rifle headspaces perfectly. No real mods, just a KAC rail and optic. Thoughts? |
|
www.ar15.com/content/manuals/TM9-1005-319-23.pdf Page 3-32 (b. INSPECTION/REPAIR] Also, a light plasma cut ring at the primers edge of the bolt face is kind of the norm, even for a bolt still servicable. |
As the round is fired, the hot/high pressures gases from the burning gunpowder seal off the primer cup to the primer pocket. During this time, some of the gases escape around the primer cup (between it and the primer pocket) before the primer cups seals off, and this plasma cuts (light layer of surface metal reaching a semi molten/high brittle carbonized state and blown away from the pressure) the bolt face to a degree each time the rifle is fired. Older case that have worn/looser primer pockets accelerate this bolt face cutting since there is a degree more time item involved in having the primer cups seal off to looser primer pockets (where talking about nano seconds here). Where you see nasty cutting is when the FP pierces the firing pin cup; with plasma cutting not only to the bolt face, but the FP tip as well. |
AR Sponsor