OK, here's the skinny on the UCL. Using a magazine from my Buckmark, which fits in the ULC like it was made for it (duh), and comparing it to a magazine from my 41, there are significant differences in size. The Browning is about .075" thinner than the S&W and the Browning is about .070" shorter (front to back, not length wise) than the S&W. So over all, the S&W is a fair amount larger overall than the Buckmark. Not an insurmountable difference if you have access to a milling machine, you say. I believe in order to make this work, you would need to remove equal amounts side to side, but all of the difference between the magazines would have to be removed from one side of the ULC's magazine bay, and that's going to just about wipe out that wall. Planning ahead, you may get by by with reinforcing the wall with something like JB Weld (a personal favorite). You may also need to reduce the size of the screw head that catches the magazine button, but that's going to be a hit or miss proposition, as the button on the S&W is small, and too much off the screw and the button won't catch like it's supposed to and too much and the magazine itself won't clear either.
Bottom line, I believe it can be done - but it won't be easy.
