I have tried to rationalize the longer chamber/short case problem, as I certainly shoot many .44 Specials - and .44 Russians - in .44 Magnum chambers. Most bigger .357/.38 bullets - even the 158gr LHPSWC - will probably bridge the gap between the .38 case and the .357 chamber's ridge before exiting the case, resulting in little lead shaving there. I really think that the differences in velocities is more a function of the b/c gap - and, even the cleanliness of the chamber exits. S&W, for example, accepts a b/c gap range of .004-.010" as acceptable. Certainly, at the upper limit of that range, lead spitting and velocity loss must be greater than at the lower end. I guess a little crud build-up around the cylinder's chamber exits might be '... a good thing'.
Whatever occurs, my 3" 65, like the 2" 10, will have the 158gr +P .38 LHPSWC's loaded... and, I'll continue to think of my 6" 66 as a .38 plinker... When I need more power, I still have my .454 SRH...
Stainz