I have an old savage 12 ga over under and it doesnt say what size the chambers are. How can I tell if it's 3" or 2 3/4". The gun was my dad's and I havent fired it since it became mine 10 years ago. I don't think my dad did the last 10 or 15 years that he had it either.

Generally, if the barrels aren't stamped with something like "For 3" shells", then it's 2 3/4" only. If you look down the barrels, you'll see the forcing cone, where the barrel's inside diameter tapers down from the .811" chamber to the .729" bore. You can measure this distance with a small ruler. It should measure 3" or a bit more from the back of the barrel to the start of the forcing cone for 3" shells.

Bye
Jack

I measured the chamber with my dial calipers and it is right at 3 inches.

As you can see your shotgun dates to 1937-43. According to my sources the 420's were chambered only for the 2 3/4 inch shells. I am not sure I would want to subject metal from that period to the pressures of a modern 3 inch magnum even if chambered for it.

http://i188.photobucket.com/albums/z271/reloader1959/ZapSnap_774.png

It's possible that someone ran a chamber reamer in the gun at some point, but.... if you want to be absolutely sure, there are chamber gages for gunsmiths that can settle the matter.

I bought some 2 3/4" Win. heavy game loads for it today I think I'll stick with those. The gun is a double trigger model too. I had no idea it was that old. I always thought it was a Stevens till I got it out the other day and looked at it.

The 3" chamber would indicate a 2 3/4" shell. The extra 1/4" is to allow room for the crimp on the shell to open.