The front band has to have some clearance to it's inner dia's to be able to slide over both the end of the bbl and the end of the mag tube during assembly.
Not very much, but enough to that the band can be slipped down intoplace w/o scratching the finish on either the bbl or the tube.
Then the band screw is supposed to pull the center section together from both sides as it is tightened up and 'clamp' the band securely around both the bbl and the tube.
The surfaces inside there may not andoften do not mate perfectly as the bbl surface and the mag tube surface is polished and can be less than a perfect circle unlike the two inner dia of the band which are machine cut and are quite accurate.
But enough of the surfaces engage and hold things tight.
What keeps the band and the mag tube from being able to be pulled forward or swiveled side to side a few degrees even when clamped is the fact that the band screw intersects both the bottom of the bbl and the top of the magazine tube when it is drilled during assembly.
This was a hand opperation in final assembly for Winchester and MArlin. Maybe in this age of precision CNC machining those small cuts are pre done on the parts and expected to line up perfectly.
The Rear Band, the one around the forend wood likewise uses a band screw that intersects both the top of the magazine tube and the bottom surface of the bbl.
When that long screw was installed (originally), the assembler gave the screw shank a very gentle bow to the center of it with a hmmer before inserting and tightening it down.
That bow or arch in the center of the shank rotated as a high spot on the shank when tightened and would press against the mag tube surface inside there to make nice and tight and help hold it securely in position.
Removing any side to side movement of the magtube at the Front Band:
If there is loosenenss in the BAnd Screw,,use that first to take up any slack. But don't over tighten as it's only a #5 machine screw (at least it was orig) and can strip out easily from the band threads.
Taking the band screw out and removing the band from the rifle/carbine, then using a wooden or even steel dowel on either side with leather safe padding to protect the finish, place in a bench vise and GENTLEy close it up to squeeze the band a very small amt . Closing up the diameters inside.
Too much and the band won't fit back on, so it takes some technique but it's a common way to tighten them up on older worn guns..
Quicky way is to place a shim inside the offending band /mag tube assembly and retighten. No harm done and a black nylon shim matl does't show. You don't need much and it doesn't have to completely encircle the mag tube as a rule.
Bubba method is to dribble Super Glue into the joint and let it set up.
Wipe away any glue that seeps out from the band joint w/acetone.
It will do the tightening, but awfully hard to disassemble when the time comes.
A common fix for guns that are loose and sent along to gunshows for sale.
