I might add that one might look at what the slug gun competitors use / used as well. They are generally just the bottom half of a now typical sled attched to the barrel with very minimal height having just enough for the barrel to clear the front rest platform.

A nice job on the rest. My only question to you and the guy who built the outriggers is what happens when you change elevation? With that flat bottom it will raise up on the front or rear edge. You need to put a radius on the bottom feet. If you look closely at the Mann the feet rotate around the center.

40 Rod

I've always had trouble with the concept of the barrel moving before the bullet leaves the barrel. 
I'm not a terrible shot. Probably average and maybe slightly better than average, on a good day.
I shoot a Pope styled CPA and offhand, especially, the recoil moves me so much that I shouldn't hit the backboard.
And bench rested that rifle is just awful, as anyone that has shot that discipline knows.
My thoughts are: my bullets must be moving slightly faster.