Torch from personal experience. CYMA is quite notorious for ridiculously tough to remove flash hiders as well. Boiled, viced, and blowdried my M14 and nothing. I used a torch (the blue ones from canadian tire) and it came off so easily it was ridiculous. It might be scary at first, but it won't damage your barrel unless you're roasting it for like 10minutes. Even then it might just char a little.
