Well, it depends on how much you need to cut. If we are talking more then 1/4" then use a copper tubing cutter, or you can buy what is called a trim die, it is basicly a die cut to caliber that allows the excess neck to stick out of the hole, you use a hacksaw to cut off the excess and trim the rest of the way to length. Otherwise just use a trimmer. What caliber are you making? Sometimes it is less hassle to just buy the stuff, or we may be able to make it for you.