The mag tube band should be tight (snug) on the barrel, with no play. There is only ONE spot on the barrel where the band should go. There are (IIRC and its been a long time) "lugs" on the barrel that fit into recesses inside the band to give proper positioning. If you carefully loosen the band so it can be slid for removal (or remove it) you'll see what I mean. Often a loose band will be because someone didn't get it in just the right spot when they tightened it up, and it shifted slightly, later, to the right spot becoming slightly loose.
Normally, slightly loose (meaning can be moved slightly with the fingers) is not any concern for function.
PLEASE use the correct size HOLLOW GROUND screwdrivers for all screws. Nothing screams "I'm an ignorant, impatient idiot with my guns" like buggered up screw slots. If you don't have a set of "gunsmith" screwdrivers, GET ONE!!!
You can get a nice, quality multi bit ratchet handle cased set from several makers, in any well stocked sporting goods store, and of course, online. They aren't very expensive, and more than well worth every penny.
I also wanted to know how far you should go in breaking down the weapon for cleaning.
The correct answer is "only as far as you
need to, and no further".
Keep in mind that "the weapon" here is the Winchester Model of 1912, and while it had a long and successful use as a military shotgun, it was never designed to be a military weapon, and was not made to endure the military's constant "field strip (or further), clean and reassemble, at every possible opportunity" style of maintenance. The fact that the model 12 was the main Army shotgun for decades is testimony to the excellence of its design's performance in a role it was never originally intended to have.
With normal use, everything you need to clean to keep the gun running 100% can be done without any takedown. That being said, breaking the gun down into its two main assemblies is something it is made to do. Full take down, done carefully, once in a while hurts nothing, but is only needed if the gun takes a dunking, or gets condensation sweats and needs to be dried out.
The Model 12 will work fine with an amazing amount of crud inside it. Designed well over a century ago it is a bit more complex than more modern designs in many ways. A different design philosophy than what is today's standard.
The unplugged magazine holds 6 (six) 12ga 2 3/4" shells. The most commonly seen old model 12s are the field grade guns without barrel ribs, most often with 30" full choke barrels. Mine is one of those, made in the early 1920s.
DO NOT USE STEEL SHOT!!!!!! EVER!!!!!!!!!!!
If you need to be shooting in an area & time when steel shot is the required legal ammo, USE A DIFFERENT GUN!
(detailed explanation on request
)
I would recommend getting an exploded view of the gun on "hardcopy", it can be very handy, and works when the power is off or the net is down....
Like many guns with over century of use, entire books have been written about them. Lots of info out there.
The takedown procedure is more complicated than a Rem 870 or Mossberg500, but its not difficult once learned. Once you have seen a video or read the instructions, come back if/when you have questions.