[RAT76]

A close up pic would help.

A long shot but do you have a rubber bumper in there? Bolt tube cover"

 

[RAT76]

I've no experience with blazer ammo but I know winchester white box would leave my S2K filthy. The blowback action of the subbie will let more crap out the ejection port than a non blowback.

I don't know what effect a weak recoil spring would have...... I've never had one.

Just throwing out ideas.