Can be done without a lathe, too.
I prefer the M die bodies over the Lee die bodies, because I don't have a lathe. I can only chuck up to 1/2" round into my drill, and the Lee explander plugs are bigger than that. A precision rotary tool with a cutting disc does the cutting, just free hand, and measuring frequently. I have turned down stock M die plugs, just chucking the threaded part into my drill. I've made my own plugs from round stock, turning down the end and threading it with a die. From memory, I believe M die plug threads are 8-32.
Don't try it with a common cordless drill though. The runout on even name brand lithium ion $200 cordless drills is typically awful.