Use a good tubing cutter with a good blade.
Make sure you really sand the pipe, it’s got a lot of oxidation on it if it’s old.
Use the sand paper that comes in a roll.
Good luck
I cut it with a brand new wheel cutter. It looks like a clean cut, and the pipe is shiny copper where I polished it. I don’t see any solder. Besides emery cloth, I used a tube cleaning brush on the outside and a fitting brush on the inside.
But now, I actually do have a small leak. And, while it started out a 1/4 turn, it is now spinning 360°. Being incompetent really sucks.
I think the leaking is because I must not have it seated properly. I really could just barely get the nut on the pipe and I put the ferrule in and hoped I could just jam them back with the valve body. I think the rotation is because I must have messed it up with my other wrench trying to hold it in place. It’s a Brasscraft and I see no good place to grab on to the body.
I guess I’ll see tomorrow if I can get the valve off without buying a compression pulling tool. If I can, that means it’s a complete botch job and the ferrule isn’t even biting. And then I’ll have to use a new one, if I can get the nut on.
Nothing can ever be easy.