I own a J-frame Centennial (640 no dash) that shot 158 grain cast bullets unacceptably low and grouped them poorly with every factory and powder/handload I tried.

Hodgdon Powder No. 27 Data Manual, in its 38 Special+P section, page 75, lists a 160 gr. JSP in front of 7.8 grains of 2400 at 910 fps/17,500 PSI. It also lists a 200 gr. LRN in front of 7.1 gr. 2400 at 890 fps/17,500 PSI.

I had some cast Valiant 180 grain TFPs that I loaded into 38 Special cases with 7.3 grains 2400, a standard small Federal pistol primer, and crimped'em in the crimping groove. Problem solved. They shoot into a ragged hole about 1/2" below p.o.a., off-hand, at 21 feet, recoil pleasantly, extract easily, and show no visible pressure signs. I haven't chronographed'em yet but will do so and report here.

They print tight groups about 2 to 3 inches high at the same distance out of my 60-9 .357 mag J-frame. It prefers 11 grains 2400 and the Lyman 358156 gc, loaded in 38 Special brass, and crimped in the forward grease groove. However, I no longer load that round for fear of my wife unknowingly loading them in her Airweight. The mag'll have to make do with loads in mag brass.

Flame away about 2400's huge ball a'fire when fired in low-light situations, but I've seen enough out of the big bullet and the old powder to take my chances. 2400 may not be everyone's 38+P powder and it aint mine in every gun I own, but it's just what the doctor ordered in this little J-frame.