[scooter22]

What he said!!! A little additional info. The tubing cutter is best as it will produce a nice square cut, BUT... It does have a characteristic of displacing some of the metal into the tube. This small ring of metal is best removed with a half-round needle file or a small paring knife. Just don't slip and slice yourself accidentally!!! You can probably guess why I warn of that potential hazard!!!
And yes Brownells still sells replacement inner mag tubes!!!
God Bless, Frank.

If your a reloader you could use your case deburing tool to remove the displaced metal.