Its obviously number one. How can they hold the trumpet while blowing if not in the beak, mouth or whatever its called.

ARs are very easily converted, but some other rifles are not so easy. Ultimately any rifle that as an automatic version will be easy to convert.

I have to say there is no such thing as a full automatic rifle. There are Automatics or Semi- Automatics! Just read it to often and started twitching lol!