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.
