Wow gents, What i meant was there is no paper work required for the stock, Take a silencer for example you can't just order one and pay with the visa and await it's arrival. The stock you can just order.
Now as for short barreled Rifle that is another discussion on it's own.
glocktalk.com has this one on some of their threads.
AGAIN I have not heard any one being arrested over this but i agree I would not want to be a test case either.
Edit to add
Glock 17 stock compatible with models: G17, G34, G22, G35, G37, G31 Glock 19 stock compatible with models: G19, G23, G38, G32 (Please specify desired model) Features: - Adjustable length for optimum comfort - Enhanced stability and accuracy to longer distances - Fast activation and quick release - Incorperated Sling mount - Light wieght construction from reinforced plastic composite ATTENTION Discliamer, If you own a Glock handgun and purchase this produt, your handgun will become classified by the ATF as a Short-Barreled Rifle. You must register your weapon with ATF before purchase of this item. Please contact the ATF directly for futher details.