Here's how I mounted mine. I drilled straight into the first crossbrace, so I could use the longest screw possible. You do NOT want to penetrate the crossbrace, or the screw will gouge the mag tube as you slide it into the forearm. I used a size 10 wood screw, 3/4" long. If I did it again I'd use a size 8. It's centered in the groove of the forearm, so it will mount at a right angle, and I tightened it with it angled up toward the port. The rear of the Matchsaver is about 1/2" in front of the receiver. You can see that based on the curvature of the inside of the forearm that there is no way the T-nut included with the Matchsaver would fit. The barrel on the SBE makes contact with the inside of the forearm, and there is no way the T-nut would work without fitting into a recess.

Screwing it on is definitely a far better feel than the velcro, but I had no trouble whatsoever port-loading with it setup on the velcro attachment. Just felt really flimsy when loading the shell into the Matchsaver that way. The adhesive on the velcro was very good: when removing it, it tore the camo pattern off the area of the forearm where it was stuck on. Good times, good times.