I'm in the process of installing a target hammer in a Model 10-5. I have before me two K-frame hammers. Both are slightly used. My question is in regard to the proper, or best contour for the bottom edge of the double-action sear. One of the sears has a rounded edge, the other is square with a slight bevel on the toe. This is the surface that engages the trigger during the first half of the double-action cycle. I'm thinking that the contour of this edge will effect the time at which the sear hands-off to the trigger cam to complete the DA cycle. Any thoughts on which is best?

The ones I have seen generally have a flat face on the bottom. That is also how the Kuhnhausen manual shows the proper cut should be. What is critical is that the transition region of the DA pull has no discontinuity where the hammer lifts too far before the trigger nose relases from the DA sear, or binding which is what happens if the DA sear doesn't lift the hammer far enough before the trigger nose slips off it. If the DA pull is smooth and continuous, don't change the sear.