Recently, I've experimented with a 6" Model 10-5, a pair of 4" Pre-10s, and a 4" 1920s Model of 1905 4th Change. The 6" gun shot 158 gr. RNFPs VERY well and to point of aim at 13 yards, so I quickly moved on to the 4" guns.
All the 4 inchers grouped the 158 grainers tightly but 3 or more inches high at 13 yards, so I loaded several powders with 125 grain TFP cast bullets in an attempt to lower the point of impact. Some of the loads were too warm, dropping the p.o.i. below the point of aim. Others printed about right, vertically. None of them grouped the TFPs NEARLY as tightly as they did the 158 gr. RNFPs. Most groups with the 125 TFps were unacceptable and the worst of the groups out of the gun from the 1920s grew to 6+ inches.
Since last week's tests, I haven't taken the time to try 125 gr. RNFPs, but have warmed my 158 gr Trail Boss load up a bit to 3.7 gr. Titegroup. This dropped the point of impact to an agreeable level out of the 4" guns.
The view from my saddle right now, is that EITHER my opinion of TFP bullets may be a little different from at least one of those above, OR my old 4" Model of 1905 and its 4" successors don't like bullets weighing 125 grains.
I'll know more this week.