I finally got a chance to sight in my Crimson Trace laser grips on my K frame revolvers: a 2.5" barreled Model 66-3, and a 3.0" barreled Model 64-3. I assumed that if I sighted in the laser grips for one pistol, it should be either dead nuts on for the other, or at a minimum, just an inch or so off. Big surprise - how about 6.0" of vertical displacement from the 3.0" inch barrel to the 2.5" barrel? I zeroed the sights for my target reloads (158gr. SWC over 4.0gr. Unique @ 740 fps (approx.) at 15 yds. for the Model 64, and then mounted them on the Model 66. I was shocked to find a nice tight group 6.0" above the point of aim. Big lesson learned was don't assume - verify. Sorry about the ****** picture, below, my computer and camera don't like each other.
Best of luck,
Dave