I think the "DIRTY" aspect of Unique - - -
- - -even the "Old" type, is highly overstated. Most of the dirty-looking thing is more like soot than real fouling. Try this test: Fire 50 or 100 rounds loaded with Unique and jacketed bullets. Use a jag tip and a snug fitting patch and run it through the barrel, WITHOUT any solvent. Repeat once if needed. See the shiny barrel? Anything that is left is metal fouling, and you'll have that with any powder you use.
Back in the days when I shot lead bullets, home cast from wheelweights, and the lubricated them with the old, soft, black Lyman Ideal lubricant, I did get a lot of smoke, and there seemed to be quite a bit of fouling. A snug dry patch took care of most of this, too, but some solvent was really better. When I began using alox-based lubes, most of that problem went away.
I'm discussing loads at moderate velocities, of course-- .45 ACP and .38 Spl, mostly. Soft bullets at much over 1000 fps, of course, left some lead deposits.
Unique is such a versatile powder, I think it is wrong to sell it short on the basis of being "Dirty." For speciality loads, wring out every bit of velocity in a magnum, there are other powders which may serve better.
Shooter973, you mention one of my favorite .357 loads. I've only chronographed the 7.0 Unique with a 162 gr. LSWC bullet, hard cast with Saeco blocks-- I used WSP primers.
Colt .357 (Pre-Trooper) 4" bbl 1074 fps
My brother's Taurus 6" 1144 fps
Accurate and pleasant to shoot. Stealthfixr, if you use this light mag load with 158 gr lead bullets, you'll probably get slightly more velocity from your M66 than I did from my Colt. That's the way it works out with other loads, comparing the colt and my M19.
Glad you're getting good results with the Berry's 124 and 5.0 Unique. You CAN run a bit hotter than that, safely, but if it works, why mess with success. If you really want to try another powder, the same bullets with 4.6 gr. of H. Universal should run about 1080 from your CZ.
Best,
Johnny