Yeah, I'll vouch for the 13 grains of Lil'Gun and a 158 grain cast bullet.
That 1500 fps is from a 24" lever action barrel though. At 40 meters it groups around an inch, give or take 0.25" depending on the day I'm having.
From my 6.5" Blackhawk the same load performs decently. At 25 yards I get 4 or 5 in 1.5" and one or two fliers, but I seem to see those fliers no matter what I'm shooting from that revolver. I'm sure I've chronographed these from the revolver but I have no recollection of the velocity. I'm sure it was at least supersonic.
Those are center-to-center groups BTW, and shot often enough to have confidence in them.
Oh, and I do get unburnt powder when fired from the revolver. Don't see it with the rifle though. I'm not one to fret over a few grains of lost powder.
I'll warn you that 13 grains is well below the 90% max for a magnum powder, however it's greater than 50% so it's not in the realm of squib loads. I did speak with Hodgdon techs about Lil'Gun and they did not recommend it for cast bullets, but didn't shudder in horror when I told them I was getting good results from 13 grains and a 158 cast bullet. The guy saw no problems with my useage.