Ed Harris
posted this
27 August 2010
Recommend that you first cast the chamber and also check twist. I'm not sure what Japanese '92s have for a chamber. Traditional SAAMI style .32-20 chamber has no cylindrical ball seat, but a 15 degree Basic (per side) transition direcltly from the outer mouth diameter of the case into the rifling. Accuracy is usually improved if you run a .30 cal. throating reamer in just a wee bit to kiss the origin of rifling and put a very slight ball seat in there. It only needs to be about .020 to .040, but as much as .080 really does no harm.
The .32-20 brass is thin, fragile and easily damaged if you are not careful. Maintain loaded cartridge neck diameter with the bullet seated at least 0.0015 smaller than the chamber neck as measured on the cast. If chamber neck is less than .328 this will limit bullet diameter to no more than .310 or so. You want a neck about .330-.332, but up to .335 as cut with a .32 H&R Magnum reamer does no harm and will let you use bullets as large as .314
For most .32-20 rifles if using a production mould I would use either Saeco #322, NEI #82 115-gr. plainbase or Lyman #3118 and try bullets as-cast and unsized, no harder than 13 BHN. You don't need to quench, wheelweights are fine, or 1 part linotype to 2 parts plumber's lead.
For rifle use only, easiest is to just fill the case nominally full of RL-7 or 4198, settled in with a long drop tube to give only slight compression as you seat the bullet. Velocity will be about 1350 with 120-gr. bullet, a bit warmer than factory, but safe in the Winchester 73 and clones and close to original blackpowder loads.
If you have a revolver also and want a load which gives dual use in rifle and revolver 3.5 grs. of Bullseye, 4.0 grs. of W231 or 4.5 grs. of Unique are fairly standard with plainbased bullets. You could also try 7-8 grs. of #2400 or 8-10 grs. of 4227, but in revolvers I've had better results with the faster powders. You may need somewhat heavier charges of those powders to get clean burning in a revolver, but I would not increase them more than a grain without changing to a gaschecked bullet. In a strong rifle you could increase maybe another grain above that, but I don't think that necessary.
73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia