I've got a BM postban with maybe 3-5K rounds through it. It's been sluggish, lately, in stripping rounds off the mag. Not short-stroking; it's just as likely to do so when using the bolt-release. Seems worse with new mags that have stronger springs. Also, when comparing it to my other BM (preban/telestock)it just doesn't seem to have as much "oomph". Like I can slowly lower the charging handle and strip a round about halfway with the preban, then let go of the charging handle and the round will chamber. With the rifle in question, it hangs up(doing this with snap-caps BTW if anyone is getting nervous reading). Anyone think a new recoil spring will help? Thanks.

Yeah, sounds like you gotta weak spring.  They might have installed one that was a little on the short side, and that might do it.  I would think they last longer than 5K rounds.  Once in a while you do get a bad one..I'm sure they didn't install a bad one on purpose.  Also check to see if the carrier is dragging on something..and that both bolts on top are tight.   Good luck.

Already checked the key/bolts and they're tight. Carrier and bolt run smooth as silk. Pass the maintenance test of drop and lock into place (from whatever disance/angle spec'ed in the manual)