Ar15 pistol

I know there are alot of gun guys like me here so I'm gonna go ahead and ask here. Do any of you have a ar pistol? I'm thinking about building one I have everything here to do it except the barrel, buffer tube and gas tube I have a extra lower and upper and tons of spare small parts. I cant decided between a 7.5 and a 10.5 inch barrel. And I am in between a 5.56 and a blackout the 556 would be alot cheaper to shoot and plink with but I think the 300 would be more suited for that short of a barrel. I would think the 5.56 out of a 7 inch barrel would loose all velocity and energy.

Just be sure you do everything in the correct order if you have other AR's. Having in your possession a short barrel and another AR is a felony. You need a specific lower designated as a pistol lower BEFORE proceeding with barrels and such.

There are certain measurements that have to fall in range for it to be a pistol. You may want to check state laws as well.

You cannot make a rifle into a pistol. BUT, and here's the weird part, once you have a pistol built you can change it over to a rifle and back to pistol form legally.

Go figure.....eh.