Sorry all, I thought that this thread was dead and haven't looked at it in quite a while.
The .50 rocks! We have fired over 200 rounds through it without a hitch. The recoil is about that of a 12 gauge, not much impact but lots of shove. We can repeatedly hit a 12" square plate at 300m with just a pistol scope. Not much left of our double thickness plates. Once I get a muzzle break on it I can put a better scope on it.
The cost was low but there were a lot of hours in it. Now that I have moved and almost have my shop up and running I am considering finding out what it takes to get a manufacturers' license. Know anyone who would like a .50 BMG for about $1200-$1500 depending on options?