Re: Looking at getting ACS stock?
No, you shouldn't have to. It should be a mil spec tube. The Mil-Spec buffer tube is 1.148" in diameter while the Commercial buffer tube is 1.168" in diameter. The mil spec tube is standard with Vltor tubes.
Just make sure you buy a Mil spec dimension ACS and not the commercial version...if it is out yet.
FWIW, the Magpul ACS is very nice. It incorporates alot of the great features of three or four of the most popular stocks on the market.
Another thing I like to do with the ACS (assuming you have a vltor tube with the witness numbers on top):
Measure from the center of the witness hole to the front edge of your Vltor Carbine stock. Put a center punch mark in the plastic on the ACS at that dimension. Then use an appropriate sized drill bit and very slowly drill a hole down through the top. Use a counter sink (by hand), round file, or sand paper rolled on a dowel...any of those will work...and round the sharp edge around the top of your new hole. It should line up nicely with the numbers on the tube and now you have the same witness marks for collapsing and extending your stock. Shouldn't even be able to tell it didn't come that way.