No, it's not a "drop in." The radius is fine. But you'll quickly notice after mounting the Brown, that the frame has two big butt cheeks that have to be ground down and matched to the curves of the new safety. Personally, I prefer the Ed Brown grip safety to all others. But takes a great deal more time, patience and skill to fit the Brown than grip-safeties that only require a .250" radius. The initial radius is the same. It's those two butt cheeks that are a pain.