Anybody shoot these in their .44 mag handguns ? I wanted to try some to work up a load at around 950 fps that has good accuracy .
I have Unique,231, and Universal .

Unique and Universal are very similar to each other and HP38/W231 are the same powders. 8.0 gr of Unique with a 250 gr lead or plated bullet should get you about 950 fps.

I don't know about the Xtreme brand of plated bullets but Berry's advises not to shoot the their brand at magnum velocities. They recommend to load at the low to mid loadings of regular jacketed bullets.

7.5-8 grains of Unique is just about in the .44 Spl area so you should be good to go. I'd check with Xtreme to get the bottom line.