Had some conversations with Dick Casull and Wayne Baker many years back, about this. Have to go dig my info on the exact measurement. But there is almost always some creep of bullet, and just a hair too much can mess you up, like what happened a while back up here in Alaska. A guy was hunting with his FA 454, and saw some cubs, and just when he thought, where is mom, she was on him. He got 3 shots off point blank, in the tumble, and the bullet jumped and tied up the 4th shot. Luckily, the bear turned and left. Nope, they didn't find the sow either. Ammo was his reloads, and after I spoke to him, he admitted it was his error with not enough crimp, and too hot a load. Did a lot of playing with this OAL, because most molds back then were for the 45 Colt longer cylinder, and the FA had a short cylinder. Only till later did these custom mold makers cut molds to your specs. As far as diameter, I've gone through 25 FA, one a 50AE, and the rest 454's. Diameter varied on the cylinder throats from as tight as .450", to some that would take a .454" bullet. Found that out back then too because only heavy bullets around were .458" bullets, and I had to size to .454" then 452" diameter, and sometimes .450" to work. Mike some bullets of different diameters if you can, and see what goes through snug.
