Here is some info I got some someone who has done this before...
Avoid a hacksaw or die grinder like the plague. I use my bench grinder with a rough stone (160 stone) for the cut. Measure it about 10 times and still cut through about 1/2" long. Use the smooth side (320 stone) and slowly roll the barrel at a VERY shallow angle around the crown to get the crown edge you want. Once you have the edge set...use a dremel with a green stone to even all the edges VERY slowly and a little bit at a time. When you have the length and crown you want then switch to 320 grit sand paper and do a finish polish on it. Clean the hell out of the barrel and finish it however you want.