2 3/4 shells can be used in barrels with marking " 3in." or 3 inch barrels. Does not work the other way around though...
50-275 USD or so
your Savage model 24S which was made from 1964-1971 is valued at between 190-275 dollars for a example with between 60%-90% of its original finish remaining,and a good bore.
It doesn't show in my blue book but I've seen 3 or 4 sell on the Internet "gunbroker" etc. for 275-300 in decent shape.
An Ithaca model 51 magnum 3 inch shotgun is worth $275-$325, depending on condition.
About 275 in good condition
This was a Savage 745C, a lighweight version of the Model 720 with a magazine that holds only 2 shells manufactured from 1940-1949. The Blue Book says the parent gun's value ranges from $110 for a well-used (60%) gun up to $275 in 100% like new condition. Trade-named guns usually bring 15-25% less than those marked with the manufacturer's name.
A 16gauge model 12 shotgun is valued at between 275-475 dollars,for a gun with between 60%-90% of its original finish remaining and a good bore.
If your Winchester model 1912 pump action shotgun,which was made in the year 1914 is a standard model model 12 shotgun with no cutts compensator attched to the barrel and has a original finish of between 60%-90%.Then you may expect to get between 275-475 dollars.
If your shotgun is new in the box(unfired) then between 275-310 dollars.
http://www.gunbroker.com/Auction/ViewItem.asp?Item=81322022
your savage model 311 double barrel is valued at between 130-275 dollars depending on condition.You can add 20% to those fiqures because it is a 20ga model.
The Savage model 2400 combination 12 gauge by .22or .308 Over/Under rifle/shotgun with 23.5" barrels and a Monte Carlo-stye stock. Made by Valmet and imported between 1975 and 1980 . Approximate values: Exc V.G. Good Fair Poor 600 525 450 350 275