The fitting of gaschecks for .45-70, and also for the .45-60 is a range of problems.
Ric is correct. The Lyman mold is tapered to use their old slip-on gascheck and can be used with the Hornady crimp-on gascheck. Several decades ago, Lyman quit offering their slip-on gascheck, going with the crimp-on design. Their bullet design criteria is for Lyman alloy (90 Pb/5 Sn/5 Sb), therefore they have a slightly larger bullet using linotype.
Talked many years ago to the RCBS engineer at a NRA Annual Meeting about mold design. His input was RCBS sells many rifle molds for many purposes, the design standardizes the size and weight for linotype. They also assume the buyer will be using the popular Hornady-style crimp-on gascheck. That is why you have the correct fit. Any bullet smaller in diameter gets into a slip-fit situation.
Also, the .45 caliber gascheck is used on pistols; thus we have .451, .452, .454, 458 nominal bore diameters to fit. Add to this the variations in cylinder throat size in revolvers, chamber leade in rifles, and the oversize bores on the Trapdoor rifle.
Back in the days of the Marston Municipal Range shooting with Ed Doonan and my first Marlin 1895 coupled with each owning a Ruger Blackhawk convertible in .45 Colt/.45 ACP, we explored gascheck to bore diameters. With revolvers using Hornady or Lyman gachecks. we found gaschecks (more Lyman) in the grass on the way to the 50 yard target. With the Marlin and Trapdoor rifles, we did not find gaschecks. Without gaschecks on the rifle loads, there was no discernible difference in accuracy, but the Marlin did lead above 1700 fps. With a Siamese Mauser full load, 2200 fps and linotype, Ed dug out a bullet stuck in the boxelder tree 200 yard backstop with the Hornady gascheck still on it after passing through the railroad tie backstop.
For the Trapdoor and subsequent single shots, I only load black powder. The alloy is 30/1 tin/lead and the bullets are soft. No gascheck bullets.
The black powder load does well on hogs and deer. The smokeless load does well also.
For .45 Colt pistols, owning a Single Action Army and New Service, I forgo any heavy loads requiring a gascheck bullet even in my Ruger Blackhawks;
- 6.5 grains Unique for the SAA and New Service using a 200 grain semi-wadcutter.
- 8.0 grains Unique for the Smith & Wessons using a 200 grain semi-wadcutter or 235 grain flat roundnose.
- 9.3 grains Unique for the Rugers using a 235 grain flat roundnose.
For the Marlin 1895, the load was RCBS 45-405-FN, wheelweight alloy, Hornady gascheck, sized .460 (only lubed as the bullet was .459+), 48 grains Reloder #7, W-W LR primer. I figured the bullet was large at the beginning and did not need too much expansion.
Farm boy from Illinois, living in the magical Pacific Northwest