Heat and a putty knife - However, please use extreme caution when removing wrap from an old drum with a heat gun. Those old adhesives can suddenly burst into flame if you're not real careful. I'm not kidding. A good buddy of mine suddenly found himself in the middle of a raging fire caused by the wrap or the adhesive reaching a combustible temperature. He held the heat gun in one place too long. So if you're going to remove the wrap using a heat gun;
1. Be in an open area. (translate, not inside the house.)
2. Have a bucket of water and some wet towels on hand. (you can throw the wet towels over the shell to smother a fire.)
3. Keep the heat gun moving. Don't hold it over one spot for too long.
If you take a few precautions, and proceed with patience and care, you'll be able to slowly pry loose the wrap in one piece, re-cut it and re-use it.
Best of luck... and most important, be safe/careful!
John