Just bought a Thompson 16-inch in .223, new but no factory paperwork, and in the rush forgot to ask about rate of twist. How do I ID that? Thanks.

Very simple, take a cleaning rod and wrap 1 piece of masking tape around the rod near the handle, but make sure the handle spins freely of the rod. Put the cleaning rod in the gun with a jag and tight patch. Insert rod until patch engages the rifling. Put an index mark on the tape and push rod until the index mark rotates 360 degrees. measure the length of rod that is inserted in the bore.

If you own a Sierra rifle reloading manual look in the very back and it give the twist rates of most rifles in the different calibers.Pistols in the revolver reloading book and your is 1-12" good Luck Reloading books have a wealth of information and can answer a lot of questions. good luck