That's not dirty! This is dirty!!!!!!!!
That's called a protective layer of crud:)
Complete thread:
- Very interesting evaluation of brass vs steel cased 5.56mm.. - 
Byron, 
2013-01-23, 10:11 
- Thanks for posting this! - 
Hobie, 
2013-01-23, 11:30
- That's not dirty!  This is dirty!!!!!!!! - 
Byron, 
2013-01-23, 12:01
- That's not dirty! This is dirty!!!!!!!! - rob, 2013-01-27, 14:48
 
 
 - That's not dirty!  This is dirty!!!!!!!! - 
Byron, 
2013-01-23, 12:01
 
 - Thanks for posting this! - 
Hobie, 
2013-01-23, 11:30