Have any of you guys had trouble with the magazine spring tension in your 550? Mine will hold 5 down but the spring seems to let the rounds slide back and forth quite a bit. Noisy if nothing else. Is there an aftermarket replacement available?

I havent had that problem, but your problem may be fixed with a mauser spring from Brownells. The CZ springs are weak, or at least the one in my 416 was.

I have the same condition with mine in 375..load the mag up and it is quiet but with only a couple in it it is noisy as hell..Should have a stronger spring I guess but I just keep the mag full when I hunt.

Ditto. I have replaced the springs with either standard Mauser 98 springs or even both the follower and spring for a Dakota 76 African.

Sometimes a simple switch of follower and/or spring (with some polishing of all critical action surfaces) can make a rough feeder smooth.

Wisners sells a good one.

My CZ as well as another Mark X Mauser work better with the heavier spring from Brownells. The MkX worked fine, but the cartridges rattled when it was carried and it bugs the hell out of me when hunting. Mine only does it when fully loaded with 5 in the magazine.

My experience with the 602 is that the cartridge on the LH side of the stacked magazine (just below the bolt) is the one that rattles. It's the second one from the top.

So mine only rattles when there are an odd number of cartridges down - specifically with 3 & 5 down. FWTW