The technique for BP isn't the same as for smokeless powder.
Honest.
First off, modern .45-70 brass has slightly less case capacity than the old balloon-head brass common before WWII. So getting even a full 70-grain load of FFg into a case behind a long bullet can be a fun proposition. Even the difference between modern brands of brass can be surprising. For example, I've found Winchester and PMC brass hold more BP than Remington, Federal and Starline.
Pyrodex has a different loading density than real BP, but should still be treated like BP with respect to loading techniques.
There are two or three things common to the BP cartridge game that smokeless loaders seldom have to employ:
1. A drop tube. This is a metal tube of cartridge diameter or smaller, 2 feet long or longer, usually brass, copper, stainless, or something else conductive (to prevent static electricity buildup). Using a drop tube to fill the cartridge case allows the BP kernels to settle more compactly with less air space between them. It's amazing how much difference in powder capacity one discovers when using a drop tube vs. just pouring powder into the case.
2. Powder compression. Compared to smokeless, Black Powder doesn't like ANY air space in the cartridge behind the bullet. Also, it tends to burn more efficiently in a cartridge load when actually compressed to some degree. So when you seat that wad or grease cookie or both, and then the bullet, you should actually be compressing the black powder column in the case a certain amount. How much is open to debate and IMHO is best determined by loading and shooting your own and tracking the results.
3. Compression die. BP cartridge rifle shooters tend to stick with cast bullets, typically of 1-20 or 1-30 alloy, which means they're fairly soft as far as cast bullets go. More on that later. Problem is, as you're seating that bullet and compressing the BP column, that nice bullet ogive ends up assuming the shape of the seating die plug, including a ring where the end of the plug sat on the bullet. There's so much force on the bullet during the seating operation as the bullet compresses the BP column that the soft bullet ends up deforming - not good. So BP cartridge rifle shooters have revisited the BP compression die, which is simply a die with stem and plunger slightly smaller than inside case diameter, set to compress the powder column
before the bullet is seated, preventing bullet deformation.
Why the soft bullets for BP? The burning characteristics of BP are basically instantaneous, the whole column explodes at once, compared to the progressive burn and gradual pressure curve of smokeless powder. (That's why cans of BP are labeled "explosive" and cans of smokeless are labeled "extremely flammable") Soft bullets tend to "bump up" or obturate upon that explosion, filling the bore and rifling better as they deform in reaction to that sudden push from behind. Add enough soft lube to keep leading down and powder fouling soft, and you have a winning combination for BP cartridge rifle loads.
Your 405gr bullets may or may not be optimized for BP cartridge loading. Cast bullet lubes for BP are different than those used for smokeless, although you can use BP lubes like SPG for both types of loads. Smokeless lubes tend to be hard, petroleum-based, and high melting point. For BP loads, you want a soft lube with low melting point, low enough to lube the bore easily on firing, yet still hard enough not to be messy on warm days. Petroleum-based bullet lubes don't always get along well with BP fouling, hence the organics usually found in BP bullet lubes.
I lube my own 530-550gr Creedmoor bullets for my 32" Sharps in .45-70, and make it from Crisco, lard, and beeswax. The idea is to keep enough lube on the bullet that you get a "lube star" on the muzzle crown after firing. That means the bullet was well-lubed all the way down the barrel, vs. running out and leading things up those last few inches. Also, if you have a well-lubed bullet and barrel, your BP fouling will remain soft, round after round. The over-powder/under-bullet wad serves an important function in keeping things clean, although their primary purpose is to prevent damage to the bullet's base. Soft fouling enhances accuracy and keeps you from having to clean the bore every so many rounds.
Good luck on your .45-70 BP cartridge endeavours, and if you need more help, by all means ask. I've started a BP cartridge primer of sorts here, with pictures, but need to finish it. I've been lazy and haven't shot my Sharps since about February.
http://www.therallypoint.org/forum/index.php?topic=421.0
