I'd recommend taking it to your local smith. The money you spend will be cheap in the long run. Let him determine the chamber length and whether it's safe to ream or not.
With piloted reamers, it's still entirely possible to "cut crooked". If you insist on reaming it out yourself-use a floating pilot reamer and go GENTLY and BE SURE to clean out the shavings often. Let it "find it's own way". Be SURE to use plenty of honing oil too. While you're at it you might as well lengthen the forcing cone too. That'll require a forcing cone reamer and always be sure to hone after any reaming in shotguns.
Honestly by the time you buy the reamers and hones it'll be cheaper to let your smith do it.
Originally Posted by m72law
i just bought an old 12gauge double barrel ''ranger'' thats all that is on the shotgun...i have read that alot of the older shotguns are chambered for 2 1/2 or 2 9/16...is there an easy way to measure the chamber without expensive tools or whatever?....also i have heard that anybody with a lil homesmithing skills can easily rechamber a shotguns chamber using a piloted chamber reamer...i have shot 2 3/4 ''bird shot'' shells in this double barrel & it seems like it has a lil more recoil then it should for a #8shot shell,thats got me thinking this old shotgun has the older chamber sizes....