Ok, I've had my Oly Arms carbine for a few months now.  I got bored on saturday and decided to order a Cavalry Arms "new-style" M4 buttstock (slider part only).  Well it came today and the short version of the story is I had to beat the damn thing off the buffer-tube with a hammer.  Although a testament to the strength of Cav's slider (not a mark on it) it still leaves me with the inferior (the new one, while it was on, felt muuuuuuch better on my shoulder and was easier to get a cheek-weld) stock piece.  My questions are:

1.  Is the Cav Arms slider for a mil-spec buffer tube?  I would assume not since it's not advertised as such.
2.  Does Oly Arms use a mil-spec buffer-tube?  I was under the impression that the only rifles which came with one was Colt and LMT, but I can't see it being a bad thing if mine has one.
3.  How does a mil-spec buffer-tube differ from a non mil-spec?  Bigger diameter?  Smaller diameter?  Is the square part on the bottom a different size?

Thanks guys!

There is a level of variance between the non-spec stocks, and while there shouldn't be, I find some of my stocks do not fit well on certain tubes.  You may find it easiest to simply order a tube from CavArms and explain what the problem was.  

I've been in the same boat as you, and all my builds now use the CMT (mil spec)stocks for the same reason you describe.

If that's the case I may just return it and pick up a CMT stock/tube from BravoCompany.....