I have two very simple questions that hopefully the gurus here can answer.

I have a lower receiver. Standard AR lower receiver. With that lower receiver, if I wanted to build it as a A.R. pistol, is that legal is there anything I’m not thinking of or anything special I need to consider?

Second question, if I wanted to use that receiver to make a 300 blackout build, is it suitable for that? I know I can put the upper on it with a bolt carrier group and charging handle I would assume but is there anything special about the lower parts kit or lower build kit that I should be buying special?

I know, I am stupid but at least I admit it and admitting it is the first step :-)