What he said! That 10/22TD you ordered is classified as a long gun, a rifle. That's what is must be forever and ever unless you want to spend the $$$ and have the BATFE re-classify it as an AOW or SBR. It's then that forever unless you again want to spend $$$. You cannot legally put a barrel on your TD with a length of less than 16" without this re-classification. Do what Crow said and look on BATFE's site. Anything you do do, get it documented by BATFE and save the document.You're treading on dangerous ground switchin a pistol to a rifle stock. I recommend researching the ATF website before doing so.