I have some experience in that regarding a 41 Mag.. but between two different revolvers: with a certain load in my 7.5" Redhawk hunter 41mag I clocked 1374 fps, while the same load in my 4 5/8" Ruger New Model Blackhawk I get 1256fps.
For a 2nd load, the 7.5" get 1409fps, the 4 5/8" gets 1286
That's a drop of 118 and 123 fps.
I'm ordering a 10" Contender bbl in 41 mag, it will be interesting to see how those 2 loads clock. Without the cylinder gap, I expect the increase to be substantial.