Shell length vs. chamber length?

Question

Say I bought a Remington 870 with a 3 1/2'' chamber. Can a 3'' or 2 3/4'' be fired from it? Thanks.

Answer 1

Yes, that gun is designed to shoot all three sizes of shells.

Answer 2

Yes, it will shoot any of the rounds you listed. The 3 1/2 inch refers to the length in the chamber that the shell has to open. If it has 3 1/2 inches, there is plenty of room for the 3 inch or the 2 3/4 inch rounds to open. So it will shoot any of them. The problems start when you try to go the other way. If your chamber only has 2 3/4 inches & you shoot a 3 inch round (and yes, it will fit), the end of the hull is trying to open up inside the consrticted area where the shot cup/wad takes up all the space. That leads to high chamber pressures. Not to mention a torn up hull. Not a safe thing to do.

If you measure a unfired 3 1/2 inch round, you will find that it is NOT 3 1/2  inches long. It is about 3 1/4 inches. The extra 1/4 inch is for the hull to have room to open. The fired hull will measure 3 1/2 inches. That is where the 3 1/2 designation comes from. The other lengths follow the same pattern. That is why a 3 inch round will fit in a 2 3/4 inch chamber but not be safe to fire.

Answer 3

Usually they can.

Answer 4

Yes, they can. Shotshells, like many revolver cartridges and a few old rifle cartridges, headspace off the rim, and are basically cylindrical from there forward. That allows the safe use of shorter cartridges in longer chambers, because the front and back sides of the rim limit the motion forward and back when they're fired. Rimless cartridges headspace off the shoulder, so they have to fit exactly between the back face of the rim and the front face of the shoulder in bottleneck cartridges. Belted cartridges headspace off the belt, which is basically a rim moved forward a little bit. If you learn the concept of headspace, you'll never again have to ask what is compatible with what.