It gets done that way sometimes. McCoy could probably do a gas cyl in his sleep. But for the rest of us, well, we MIGHT be able to get to the top key with a tool made to do it. The side keys, how do you spell headache? Hate to disappoint purists, but peening the barrel's splines just comes with the territory. START with the top one, maybe it'll be enough.
I had the honor to watch Don McCoy peen many a barrel for mine and others M1's-match grade and blasters alike. He laid the front end of the barrel on a shot filled leather bag, took the ball end of a hammer to the grooves, and flailed away. First few times I saw him do that, I literally winced with each blow. Then to install the cylinder, he would use a short piece of medium diameter brass rod with a hole bored through that would clear the barrel and used the same hammer to install the cylinder. But then, he had decades of experience at it, so YMMV.
Well, my local old time smith peened the barrel for me today - with a ball peen hammer. But he's done a jillion of 'em. I watched him do it and was glad he had the hammer and not me. Still, I might be able to do it the next time. Cylinder is tight, all is right with the world. Going shooting tomorrow.
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