This has been suggested befo', as BHO says, but I'll repeat it here. A lathe is cetainly not necessary to make a chamber gauge or set of gauges. I bought a half dozen stainless steel rulers at a yard sale, several years ago. By narrowing the ruler to the width you want, for 3-4", you will have a very inexpensive chamber gauge. The same could be made out of brass or aluminum flat stock but the rulers have the advantage of having the numbers on them already. you insert the gauge as far as it will go, read the numbers at the breech end of the barrel(s). It will stop at the beginning of the forcing cone(end of the chamber). The number you see is the chamber length.
