DavieKing,
I have no experience hot rodding the .38-55 cartridge. Your loads when placed on a graph showing fps per grain of powder give the appearance you have reached a practical maximum with this powder at 30.0 grains of powder. As you shoot groups with these loads I�ll be interested in reading of the difference in accuracy between the 29.0 and the 30.0 grain load. Just to see which load your barrel likes.
If you�re Library has a copy of the 1968 Edition of the Gun Digest (22cnd Edition) look up an article by Christian Helbig: �The .444 Marlin and its Big Bore Brothers.� Helbig was quite an experimenter with the .38-55 and regularly loaded the 255 grain bullets to 1850 fps in a 20� barrel using Hercules Hi Vel No. 2.
I also look forward to seeing your case measurements. Are you measuring the case head or the pressure ring? I have found pressure ring measurements (PRE) to be useful in establishing stop points.
