Hence the reason I went with the stand-alone mount for my system.
I sold the upper that I'd been using as a mount a while ago, and found that the launcher had sat on my bench/on top of my safe for over a year without being fired.
So, I decided to dig through the pile of steel beside my lathe and see what I might turn up.
I found a couple of chunks of steel appropriate for the task, total value on the steel was about $14 (in it's raw form) and then spent about 20 hours in front of the mill with it turning out the system you see below:
The first cut:
Return pass to finish the cut.
Clamped on a 45 to cut the angled side of the picatinny rail:
Cutting the picatinny slots:
A full length rail takes about 5 minutes per slot (2 passes) times 29 slots = a bit over 2.5 hours just to mill the slots.
I don't have a 1.125" drill bit, so I started small, and ended with working my way up in size on the lathe. This was a SLOW process due to the offset setup....going fast would probably have ended up tossing the piece out of the lathe.
Cutting the area out for the pistol grip:
1/4-28 tap for the pistol grip.
Completed, but not welded yet: