Duncan;
I'm in the same boat as you. I have a pound of FFFFg, and only one pistol to shoot it in, an NAA mini. At 5 grains a shot, a pound is going to last a while.
I know that North-South Skirmish Association shooters often shoot reduced loads of FFFg in their .58 caliber rifles. The ratio of performance is that a 60% reduction in charge for FFFG equates to a full charge of FFg. Apparently, 45 grains of FFFg leads to less fouling and more consistent groups.
I've wondered if a similar conversion could be applied between FFFg and FFFFg for use in pistols. Pressure is a tricky matter though. I have an old Sam Fadala book of black powder loads, and he tests 40 grs. of FFFFg in a ruger old army, and everything turned out fine, except accuracy suffered. I have an ROA, and I'm not worried about blowing it up. I'm an accuracy guy, so I'd be starting way low to find the sweet spot.
Secondly, in terms of duplex loads, the way to do that is to have layers of powder, not mixes. It's a specialized field when mixing smokeless or smokeless and black, since you can easily blow yourself up. However, I think loading, say, 15 grs of FFFg and 5 grs of FFFFg for a final "kicker" to maximize velocity might be an interesting expiriment. The trick is to load it as you would powder and a corn meal filler. In layers.
-John
