my buddy has a sig swat that came with a ctr none folder, will any mil spec magpul stock fit on that tube or is it a sig specific ctr?
If your referring to the model with the M4 buffer tube AKA(ER or DMR) lower, then any commercial stock will fit it. Does it look like this:

Mine came with a milspec...
Yea I just called him, thanks for clearing it up. He was certain it was Mil spec but it turns out his commercial stock did fit on it.