sjmjax, my groups with several 4" Model 10s are similar to the results from your 4" guns. I've had to switch to 125 gr. bullets and use a center hold with some guns and a six o'clock hold with others to get the bullets to impact in the 10 ring.

I've noticed others on this forum reporting good results when they used 158 gr. bullets in their 4" guns. My notes show at 15 yards they strike 4 to six inches high out of the 4" guns I've tested this summer but shoot to point of aim out of the 6" Colt OP and strike about two inches above p.o.a. out of my 6" Model 10-5.

The three Pre-10s whose serial #s reflect a b-date of 1946-1953 have all shot to point of aim and grouped tightly with a 125 gr. bullet travelling about 900 fps.

Obviously, YMMV,

Rich