Nah - the innards are the same, the difference is in the stock configuration/barrel rib etc... But the mechanics are the same..
In '79 Rem made a bunch of changes to the M1100 - using a 2 3/4 magnum in a standard chamber will give excess gas pressure to the bolt/receiver and will, over time, cause damage.. If the owner swaps the barrel over to a magnum barrel there's one less gas port to contend with and will alleviate the pressure..
I've had a couple 1100 (and the M58 Sportsman it replaced) in with damaged (read: sprung) receivers from guys using the magnum shells in a non-magnum barrel..
Yesterday, in fact, a M1100 came in with a 'new' barrel and the bolt would close but NOT open.. I noted this was a pre '79 model using a post '79 barrel. The bolt body and locking bolt had to be 'fitted' to the extension in order for it to work properly..
It's just something to note and remember when/if switching barrels on older models..
