load reduction

[Ken G]

What's the typical charge reduction when going for 2F to 3F to get the same velocity / barrel pressure? 

Ken

[Eric Laird]

Ken,
Don't hold me to it, and it probably varies by brand of powder, but I seem to recall that the general rule of thumb is about 15%. If I can find my old Lyman Blackpowder Manual, I'll check and let you know. Now, If I could just remember where it is!
Eric

[Ken G]

I did not think about it being different for different manufacturers.  Good point.  I'm using Goex.
Ken

[roundball]

What's the typical charge reduction when going for 2F to 3F to get the same velocity / barrel pressure? 

Ken

I use Goex and normally go by the 10% reduction factor

[Dphariss]

What's the typical charge reduction when going for 2F to 3F to get the same velocity / barrel pressure? 

Ken

You will likely not get the same pressure/velocity.  FFFG may be slightly higher at the same velocity.
But I would not be concerned. I used to shoot 100 gr of FFFG Goex  in a 54. I currently use 90gr of Swiss FFFG.  50 used to use 90 goex currently shooting 75 Swiss but development is not complete. Generally smaller bores need more powder vs ball weight.
FFFG may shoot better and generally shoots cleaner.

Dan