Originally Posted by BigDinFL
IF, and only IF, the gun is properly checked and passed, then going to RST or Polywad for "Vintager" loads in your proper chambering - most likely 2-1/2"- would be the safe way to go. Those loads are VERY low pressure designed for these older guns that have been deemed safe by a qualified gunSMITH - not some parts changer.
A gun that old, I would bet, also has the shorter chamber, something that qualified gunSMITH can tell you.
Remember, the length of a shell is the fired length - an unfired 2-3/4 shell will fit into the 2.5 inch gun, but upon firing, the petals will open in the forcing cone raising pressures to dangerous levels. Even if your gun does not explode, you will be beating the gun to death and end its life prematurely
All of that is absolutely true. But it also misses the point.
The point is that the gun can fire still manufactured, commercially available ammunition.
And that means it's not an antique for the purposes of the NFA, so cutting down the barrels shorter than 18 inches would make the OP eligible for ten years in a federal prison, a $250,000 fine and lifetime loss of gun rights.