HK91 bolt staining?

hi guys,

recently bought a HK91. 1981 date code (IB).

anybody know what the dark staining is on the bolt? tried to scrub it off with a brass brush. doesn’t really come off.

should the bolt date code match the receiver date code?

thx.

Might want to post this stuff a little further down the page - you’re still in AR territory here.

ah wrong section thx.