The reason a frame or receiver is transferred as "other" is precisely because it does not meet the definition of "rifle" or "pistol" and could be built as either.

Quote Originally Posted by DS-11B View Post
I don't think you have anything to worry about though but just realize that there really isn't any DEFINITIVE interpretation of the law, especially when it comes to AR pistols.
I don't see the need for ATF interpretation, the definition of a rifle, pistol, shotgun, frame or receiver, etc. are simply stated in the law.