I have a couple of Black Diamonds and, like Rick Reno, have had pretty good luck with the 350 gr. Maxi-Hunters using Pyrodex Select. I use 100 grains with a Wonder Wad at the base of the bullet. Either of my BD's will shoot 3" to 4" at 100 yards with this load. It performs pretty good on deer sized game.

To be honest, I can't recall any MZ bullet ever shooting as badly as 6" to 7" at 25yards. Have a snub-nose five-shot .38 that will shoot that well . . . . Got to be something whacky going on here.