44 special and black powder ......?

[the Black Spot]

So I loaded some 2f and 3f under a 255 gr cast bullet and was wondering on some velocities:
20 gr of 2f
25 gr of 2f
20 gr of 3f
25 gr of 3f

7.5" barrel

Anyone have a good guess or know ? Thanks

 

[Jaymo]

What barrel length?

 

[the Black Spot]

I added barrel length in first post