I can't imagine any reason why they would be illegal to use for hunting. Unfortunately, in this country suppressors are often viewed as something only people up to no good have, and it makes no sense at all.
I think in Scotland if you are on a guided hunt you have to use a suppressor on your rifle. I could be wrong, though.
Pretty much all you have to do to get one is pay for the $200 tax stamp to legally own one.
Scorpion, pretty sure you are correct about the Scotland thing. Was watching a show on the Discovery channel the other night about a guy hunting in Scotland and he used a suppressed rifle. Thats what made me think about it.
They can be purchased with a little extra paperwork in most states (PA being one that allows them). You'll need to have your local Chief Law Enforcement sign off unless you buy as a trust or a coroporation. Some CLEO's may not sign off. It is wise to check before staring the process. If they won't sign, you can form a trust and circumvent the need for their approval. On a hunting rifle with high velocity ammo, they do reduce the noise and muzzle blast from the shooter's perspective. There will still a loud crack as the bullet goes supersonic downrange. You can use subsonic ammo, but that obviously limits the range and killing power. For subsonic hunting, something like a 44 mag rifle or 458 SOCOM is often used since you can shoot very heavy bullets that will give you sufficient killing power even when subsonic. Even subsonic, most supressed rifles and handguns sound like a air nailer. The stuff you see in the movies is pure Hollywood fantasy.
They are not required in scotland and England, but most hunters use them. You can safely shoot without ear protection when you're using a moderator (as they are called over here). The bark of a big gun turns into a crack like a high velocity 22. Subsonics are basically whisper quiet. I have one on my 22 and also shoot it on my 17 hornet. If I move back to PA, I will have one for my guns. If I'm stuck in NY or NJ, then I'm stuck without one as neither state permits them.