I have a new Chiappa M92, .44 magnum. I shot only two 5 shot groups with it, to confirm sighting and function to begin with. Then I installed a set of Uncle Mike's sling swivels, including a front barrel band style one that goes over the magazine tube. I re-installed everything after, and now am wondering how tight the screw should be that goes between magazine tube & barrel, through the band. Tight as it goes, or something less? I took 5 shots after, but with different ammo, and accuracy seems much poorer.

Different ammo? You have too many variables involved to make any conclusion.
How tight? Tight enough to keep it in place; don't strip the threads. There are so many things hanging off of a lever action barrel that I'm not sure it matters.

It turns out it was the ammo I used after putting the swivel on, not the barrel band. I shot some different loads with it today that were a nice tight group, right at point of aim.

Id put a little locktite on it and snug it up tight as possible without stripping threads or messing up the screw head..

Thanks Ray, I had done that already, just wondering if I'd overdone it!

You should be good. I at least haven't seen much change after installing a sling swivel band.

Sometimes you can dabbly with screws and make a gun shoot better or worse, you just have to try it at full to half turns, but Id stop if it shoots and inch or so at 50 yards..and that depends on whatcha intend to use it for..Neat little gun.

Ray is right, snug then some locktitr. I stripped the threads on my Trapper once.