Is there any rule of thumb regarding the increase in velocity as the barrel/cylinder gap is reduced? I would imagine that the velocity increase per 0.001” bc reduction would vary depending on whether it was from 0.008” to 0.007” or from 0.003” to 0.002” since the reduction from 0.003” to 0.002” is a greater percentage reduction than that same 0.001” increment at the larger bc gap. I have a Ruger Bisley 45 Colt and it has 0.008” gap and I am getting 1200 fps from a hard cast 335 grain bullet. What would the velocity likely be if the bc gap was reduced to 0.003”? Thanks, Rufous.

I would expect a tighter gap would improve velocity, but how much I do not know. I think it would depend upon the tightness of the chamber and barrel dimensions.