is your stamp for an SBR?  then i don't see why it would be wrong... but my stamp was for the can.  the thingiemabob i have on there is a sig sauer pistol brace, not a buttstock.  my AR is considered a pistol, which is why i have a short barrel, but brace instead of stock.  hit me up if you have questions, i'll answer the best i can: jinustuff   gmail