Cheesewhiz: It's not the hammer. My 75B has the stock hammer that fully clears the sight.
Since I replaced this sight I've reloaded and shot maybe 4000 rds as a guess.
The first sight , as CZ Custom said, didn't quite clear the slide. It had two small rub marks on the bottom side of the rear comp sight (that broke off); SOoo what they said made sense. When I replaced this one, I lightly sanded the ribbed area under the rear of the sight until it completely cleared. 5-6 months later it broke in exactly the same place as the first one did. This one bounced off my cheek and I never found it.
One thing I did notice before it separated, I was shooting way high. I couldn't hit a popper at 10 yards- for 3 or four shots I was shooting just above it. That means the sight was bending UP before it snapped off.
When I replaced the first one, there was at least one other poster who had the same thing happen.
I've also emailed CZ CUstom shop about this on 2 Dec., and haven't had a reply yet.
I can borrow my son's Shadow (

) , but I'm getting a little frustrated with this. I don't want to repeat this again--maybe it's something I'm doing, but I don't think so.