I have Trail Boss on the way, and some PRVI 150gr. 0.311" FMJ Boat Tail bullets coming too. I checked a Montana bullet works twist rate tables and maximum weight bullet a 0.311" bore 1 in 18 twist will stabilize is 144 grains. Maximum length of bullet is 0.810".
I will be at or slightly exceeding max recommendations of both, but I really wanted the boat tail bullet not that BC matters inside 125 yards (max range) but I figure every little bit counts for something. I did a trajectory comparison between various 123gr and 150gr bullets of different BC and the difference isn't enough to matter.
My goal is to have the most accurate load possible with these boat tails and "fuller" case of powder for consistency (bulky trailboss). Another perk of the trailboss, since 150gr is not a bullet intended for the 32-20, the instructed method of powder calculation from IMR is handy! (70% of remaining case capacity AFTER calculating bullet seating depth)
I'm really looking forward to this. I hope it works out.