I use an old RCBS mold for 148 Grain BBWC's. Wheel-weight lead with about 5% added tin provides bullets that cast beautifully at 143 to 144 grains. My goal with these bullets is "X-Ring" accuracy at 25 yards with the least recoil possible for our Bullseye matches.
Using 3.3 grains of Bullseye in .357 Mag cases, I've seen the following average velocities:
- 6" GP100 = 813 fps
- 4" GP100 = 781 fps
- 3" SP101 = 755 fps
I get great groups as the charge of Bullseye goes up, but 3.3 grains is the least amount (i.e., the lowest recoil) I have found to give consistently excellent groups from .357 Mag cases. An "excellent" group for me is 6-shots into less than 2", c-t-c, at 25 yards from sandbags with the 6" GP100. I shoot the 3" SP101 sometimes, "just for fun," and get 25-yard groups of less than 3" with this load.
The 3.3 grains of Bullseye with my cast bullets in .357 Mag cases gives a small amount of forcing cone leading, a clean bore, and black bullet lube soot all over the gun which wipes off with a few drops of solvent on a rag.
After using Bullseye since the 60's, I just started experimenting with HP-38 and find it flows like water through my powder drop, drops very consistent charges, and give "almost" as good of groups as Bullseye.
When I get my chronograph working again, I'll have another go at HP-38, but it appears to need a tiny bit more powder than Bullseye to get about the same size groups and velocity. I need more time to experiment before making up my mind on HP-38, but from what I've seen, I like it too:-)
In response to your question about the distance for shooting wadcutter loads, I shoot slow-fire at 50 yards and timed- and rapid-fire at 25 yards. The "X-Ring" on an NRA target is about 1.6" so I strive to keep my "sand bag group size" at less than 2".
On a good day with the 6" GP100, I have had 6-shot groups that averaged about 1.5" at 25 yards with my cast bullets. The best I've ever done with store-bought HBWC bullets is about 2" at 25 yards (and I've always had some amount of barrel leading with the HBWC's). By the way, my bullets make neat round holes in the target while I've never had store-bought HBWC's that did not keyhole a bit from every revolver I've ever owned.
JMHO - YRMV