: I bought a very old sp1 that I'd like to rebuild. Is it ok for me to put a new preban M4 upper on it and a 6pos stock?
 I know I can replace the sp1 barrel and internals but I'm not quite sure it's legal to totally rebuild this from a stripped lower. Has anyone had any experience with this sort of thing before?
 Thanks for any help you can offer:)

Did you purchase it as an assembled rifle or just the stripped lower?

Don't listen to this guy.  If it's a Colt SP1, it's a preban and you can do anything you want to it in terms of barrels, flash hiders, telescoping stocks, etc.

There are people on this board who want to play unrealistic, hypothetical, legal mind games about how if you took a pre-ban lower apart for one day and sold it, the lower somehow reverts to forever being a post-ban, etc.  But this is all nothing but mental masturbation.  Ignore these idiots.

A Colt SP1 lower is pre-ban.  Period.

I disagree. Somewhat.

Allow me to explain. the ATF has ruled that a stripped lower cannot be an assault weapon. That is a fact. IF you sell a stripped lower, you are not selling an assault weapon. Therefore, there is no such thing as a pre-ban lower.

HOWEVER, there is one exception. A lower marked COLT AR-15.

the name COLT AR-15 was banned. IF you have a lower marked as such, it need not be assembled. The stamp alone makes it an assault weapon.


So, your SP1 lower should be marked COLT and AR-15 (mine is). If so, it is pre-ban, unreputedly.

Bottom line: If your lower has Colt AR-15 stamped on the side, You can put on all the nasty features your heart desires. Bayonet lug, FH, threads, Grenade launcher, Swiss Army Electronic Lighted Can Opener. Have at it!

: Yes I bought it as a whole rifle. It can be very confusing the way people split hairs on this issue. I'll keep all the old parts to be safe anyway.