The 1100 mag shoots 3in. shells, the 1100 standard shoots 2 3/4in. shells.
Size of the projectile
If the gun is marked 2-3/4 on the barrel, that is the maximum length shell that the gun will shoot.
Not much. A few more years of R&D, better material.
Have it examined by a competent gunsmith to be sure
Case dimensions
Bla kaung mag research!
whether or not it has the BOSS or not, roughly between 1100 and 1300 dollars Canadian
Size and amount of propellant
Basically the case is all. Same caliber bullet, but the case is shorter in the ultra mag. Its basically just a smaller round, bigger punch.
The difference is that the Remington 1100 3 inch mag will take three inch mangnum loads and shorter where one that doesn't say 3 inch on the barrel will only take two and three quarter inch shotshells or smaller.Trying to put a three inch inch a gun that is not designed to will cause extreme stress on the barrel and will get jamed in a pump or automatic shotgun.
357 case is @ 1/10 of an inch longer.
In great condition this gun is valued between $1100 and $1800. BlueBook has it at $1100 but then add several hundred dollar for being a Deluxe and a 300 Win Mag Cal. Search Gun broker.com and ebang.com for similar items. But, don't get confused on lesser models priced at $700.