Got my double star lower today and it looks great.  Matches the colt upper very nicely and looks great.  I also found a used M4 Socom stock for 100 bucks last night so thats on its way.  My issue is the rear take down pin just falls out.  The holes on the upper and the lower match perfectly the pin slides in but will just fall out.  Whats the best pin?  The anti walk, Screw type,  or the expanding one I saw somewhere.  Its a 6520 upper.  Also best price and source to have my barrel threaded for a flash hider.  I'll have pics soon to share.  Its my budget build and with the Socom stock I'll be in it 500.00 even.  I also have an old military C1 stock that I'll like to make usable.  I have the stock only.  Is there a source for the tube, buffer, spring, and screws?  

Did you remember to install the detent and spring on the rear takedown pin?  Bushmaster sells the stock parts.

No I'm an idiot.  I don't have the stock yet so of course I don't have those parts in.  They all came in a little bag with the lower.  Its my first build so I guess I didn't realize how that worked.