AAAAAUGH! Simple answer, but I'm still stuck.
I called Lauer and spoke to the guy that answered the phone- great guy!
He said that he had been working on a display rifle for Lauer to show off their products and was having the same trouble with an M6 light and the rail. He went and got the rail and light to verify. He asked me if I had the box that the M3 came in, which I thought was an odd question. He said he thought there was a spare spring loaded "post" that fits inside the rail channel included in the box. He went to get his, swapped it out in the M6, and VIOLA! A very snug fit!
Apparently the light comes with a weaver spec post installed and an M1913 post if needed.
Except I'm in OHIO and my box (with the spare post, perhaps?) is in KANSAS!
Any one have an idea of where I can get a spare post?
Anyone have an unused one I could buy from them??? a BIG +1 for the guys a LAUER
they are great! I ordered on Friday afternoon and got my rail in the mail today, and the guy on the phone went out of his way to help me figure out the problem (at 8PM EST)