What is the question?

First, 6 round samples are not statistically significant. You really nee to fire at least 20 round samples to be even reasonably confident in the data obtained.

Second, velocity results from different guns mean nothing when compared with each other. I have .38 Spl and .357 Magnum revolvers ranging from 2" to 6 1/2". Often my 4" guns will show higher velocity with the same load than any of my 6 and 6 1/2" guns! It will take chronographing hundreds of rounds in each gun to make a significant observation of the relative velocity potential of each of your revolvers.