After reading a few posts from other sites, I have found the people still use torches to heat their Nitrous bottles.
DO NOT DO THIS. Even if you keep the torch moving, you can still weaken the structure of the bottle. Here are some pictures of a bottle explosion. This bottle was
NOT heated with a torch, it failed on its own(yes it can happen), that is why bottles have to be recertified, but why help it fail with a torch.
Use only warm water, air, heating pad, or bottle warmer, and watch your bottle pressure.