A "light" squirt of gun oil into the port will be blown out over the next several rounds, and will mitgate hard carbon buildup as firing progresses.
Once firing is done, the bolt can be disassembled and literally wiped clean. (You'd be amazed)
Bill Alexander (of the Grendel) advised me in favor a "wet-bolt" shooting -- which is the near exact opposite of what I'd normally do in combat/field/dusty circumstances. But once firing starts, it's incredibly effective at preventing stoppages and cleanup.
(postscript: I hate steel cases.)