Starting Out
I custom tailor my loads for the Trapper to match with the sixgun I am using alongside. However, none of these loads should be taken for granted and should be worked up very carefully. For example with the 4-5/8" Ruger Blackhawk, I use the NEI 310-grain Keith bullet over 21.0 grains of WW296 or H110 for 1,125 fps in the sixgun and 1,445 fps from the Trapper Barrel. I certainly don’t know of anything in the lower 48 that cannot be handled with this load.
Before loading any ammunition for leverguns, I first make dummy rounds to be able to check both feeding through the action and chambering. It takes at least two rounds to be able to see if the rounds are too long to accomplish both operations. I found the following heavyweight bullets all would work through both the Winchester and Marlin actions: NEI 310 Keith, NEI 325 Keith, Lyman #454629GC 300-grain FN, RCBS #45-270 SAA weighing around 284 grains with my alloy, and I also checked the #454490GC design by Ray Thompson, which is a 255-grain Keith-style gas-checked bullet. All of the Keith-style bullets mentioned feed and chamber even though they have shoulders in front of the case. However, I crimp the #45-270 over the front band to ensure trouble-free feeding. None of these loads will work through the action of my Rossi .45 Colt Model 92.