An XP 100 should already be registered as a Pistol. If you purchased it used it should have been transferred thru an FFL. But to answer your question. Yes, it doesn't matter what kind of stock it has. The barrel length is the deciding factor between pistol/handgun or rifle. A rifle barrel has to be 16" or longer to be legal. A pistol/handgun is 16" or less. It is highly illegal to possess a rifle with a barrel length less than 16".