So I bought this Officers upper off the internet. It looked great for what I paid. I did a little research, and found that the frames were nearly the same, no matter which size you used, and found that it fit the frame I had purchased from Sarco best of the four frames I had. I took it to the gunsmith friend for final fitting, and it fits now with NO slack. It does hang over the back slightly, but that I don't care about. At the range, it has performed from the first shot. I have used ball to start, then switched to XTP hollow points. So far, it has never failed in any way, (knock wood) and it is plenty accurate for head shots at 15 yds. (That's the gun, not me.) Boy, am I pleased. The drawback is that my P12 is just as reliable, and accurate, and is lighter to carry. (A few more rounds, and if there are no problems, I'm going to start carrying it anyway.----------