I've got a question regarding the Sig SB-15 brace I'm hoping to get some opinions on.

I have a friend with a Century Arms C93 pistol. He was wondering whether or not you can put an AR pistol buffer tube and Sig Tac SB-15 on it. He had read a discussion on another forum (don't know which one) where there was a difference of opinion because the C93 didn't use an AR buffer tube to begin with. Some people were saying that by adding the buffer tube to the C93, you would be violating NFA laws.

My first response to him was to write the ATF and ask, but I would still like to hear peoples thoughts. Are you allowed to add a part to be able to use the SB-15?

Thanks for any thoughts.