Have one on my newest build. Love the feel, but it doesn't hold in place. I have tightened the tension screw, but it always seems to losen.
Any ideas?

Pardon me, but what tension screw?  I have SOPMOD in my hands right now.

There is one on the bottom of the screw on the release leaver, I'm holding one as well.

Is the roll pin through the nut/screw missing?

That's a good question. This is my 1st sopmod stock so i dont know how it's supposed to be.

That is not a tension screw.  I am assuming he is referring to the tension of the stock against the buffer tube.  Correct me if I am wrong, that screw is used to set the amount the locking pin moves in and out of the holes on the buffer tube.  You can turn that screw in to where the stock will not move when the locking lever is pressed.  

I am assuming the OP is referring to the stock being loose on the buffer tube, as we all know the SOPMOD stocks are very tight on the buffer tube, unlike the cheaper commercial of mil spec M4 stocks.  

77

I'm thinking incompatible buffer tube (dimensions)

A photograph would help us understand as to what screw you are referring.

hmm, could be buffer size.

the stock locks in place for shouldering, but after shooting, it collapses right back in

Not sure it is the buffer size, as SOPMODs are on the military size, 1.14" and if it were a commercial tube, 1.17, the SOPMOD would not slide on.  The screw on the bottom adjust the depth of the engagement of the pin that locks into the extension tube holes.  Once the adjustment is set, proper depth, there is a roll pin that keeps the screw from backing out or in, keeps the depth correct.

Can you measure the extension tube dimensions?  

Is the extension tube new?  Excessive wear in or around the holes?

This is baffling, please post pictures, so we can see what is going on.  This screw is the only screw on the entire butt stock.

77

I have 3 LMT SOPMODs and they are all pretty snug.