darkroomdan,
I shoot the 358429 (approximately 175 grains) in a Smith Victory series handgun—an older one for sure. I can get around 800 fps (a bit less) with no signs of pressure—I haven’t pushed it more because of the age of the handgun. 850 fps might be pushing the pressure curve a bit...
Regardless, I think you might do better with a slower burning powder. I use Blue Dot, AL-8, 2400, and sometimes 571, the fastest of what I have listed. I get the best accuracy with the ol’ AL-8, but those big yellow-green flakes don’t meter worth a darn!!! Still, I think I would pursue slower powders than Unique. Good-luck…BCB