I just received the Beartooth Bullet fire lapping kit for my 45-70. It says to use a reduced load.
I have no idea what to load that would get the bullet out of the barrel but not be too fast? Does anyone have any recommendations?
Sure do. With either Red Dot or Bullseye, around 4 to 5 grains should easily do it. Maybe less. If you fill the case with polyester pillow stuffing (dacron) after putting in the powder, it helps clean the bore and you can use less powder. By "fill the case with dacron" I mean stuff as much as you can in there. Probably will end up with 10-12 grains of Dacron on top of the powder, if you get ambitious and weigh the stuff.
I wouldn't go any slower than some thing like Unique, and I'm not 100% how it would work.
I haven't lapped a .45-70, but have done many different rifles in that case range. As an example the .444 Marlin will put lapping loads out the barrel at around 3 grains of Bullseye, with the rest of the case stuffed full of Dacron.
Good luck. Be prepared to stick a bullet or two, it happens. Make sure each one exits the barrel. Don't try to use the brass for anything else when done, it will be contaminated with abrasive.
In theory, you are looking for airgun velocities that just barely get the bullet out of the tube. This is because they are driven by pressures low enough that they don't significantly upset the bullet. Significant bullet upset after passing through a constriction laps both the constriction and the wider diameters after it, which would not be useful until the polishing stage.
Use of the polyester pillow stuffing is important, in my view. Though exceedingly rare, there is one report on the Finnish Gunwriter's site of a detonation of about three grains of N320 (about like Bullseye in burning rate) in a .308 lead bullet load. Using the pillow stuffing to take up empty space and keep the powder against the flash hole prevents that pretty positively (insofar as anyone understands the detonation phenomenon's apparent need for empty space).
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