I have and love my Sig 516 without a doubt a well worth investment!!
Does anyone know if it has a Milspec or Commerical Buffer tube?
I want to change it from Black to the Magpul OD stock.
It must be commercial because I bought a Mil Spce Mag Pull and it fit to tight.
Mine came with a Mil-Spec buffer tuber.
I can confirm that it is a mil-spec buffer tube because I bought a commercial spec Magpul ACS stock (which is now for sale) by mistake (the first position has a little play, but all other positions fit tight and snug). You can visually see for yourself if you remove the butt stock and view the back end of the tube (mil-spec is flat and commercial has a 5° slant):
You know you could just paint it OD green and save the $$$....