RSJ...what is this downloaded load you speak of? I just bought dies, and mold for my MH. I would love to find a downloaded...AKA cheap...load for it.
Essentially, I am trying to approximate the Martini-Henry "carbine load" introduced in 1877 ... it having been found that the M-H carbines were virtually unusable with the full rifle load of 480 grain bullet and 85 grains powder (... ask Guns Garrett and his poor shoulder about that!) This called for a shorter 410 grain bullet, so the 405gr bullet is darned close (... although they are a bit too small in diameter, so I cast them quite soft so they "bump up" better in the rifling, and shoot them unsized as well) and 70 grains of powder. Essentially the same load as the ultimate .45-70 loading, you'll note.
The difficulty is that although the original full 85 grain rifle charge came all the way up to the bottom of the cartridge neck, the level of 70 grains of powder falls below the shoulder of the Martini-Henry case. They originally used a quantity of carded wool below the "glazed disk" in the carbine load, to take up the space, then later the carbine load cases were instead lined with a coil of heavy paper/light cardboard below the shoulder.
Unfortunately, "modern" commonly employed fillers (like cornmeal, seminola, grits or whatever) may be problematic because they can reportedly "slug up" in the bottleneck, resulting in erratic pressures and potential loss of accuracy (if not dangerous overpressure.) The solution is to use an "active filler" (a 50/50 mix of black powder and the cornmeal or other filler) over a reduced powder charge. The BP within the filler theoretically burns as soon as the powder charge goes off and prevents "slugging" of the filler in the neck. Technically, you have to include the BP within the filler as part of your powder charge, so I use about 55 grains of 2F topped by 30 grain equivalent (by volume) of the 50/50 "active" filler - this pretty much duplicates the
volume of an 85 grain charge, while yielding an "actual" charge of 70 grains BP (i.e. 55 + 15).
I also use a "grease cookie" (a disk of good soft BP lube, such as SPG or homemade equivalent, sandwiched between disks punched out of coated milk carton material) directly under the bullet, in place of the beeswax wad and glazed cardboard disks of the original loads, to help keep fouling soft through a course of firing without cleaning, such as we do in GAF skirmishes ...
Here is a graphic, based on the period cross-section of a full rifle load in a drawn brass case, on the right, to illustrate my adaptation ...
I use similar construction for my .577 Snider-Enfield cartridges although, since they have a straight-walled case, a plain filler can be used in lieu of the "active" filler. Although it may increase competition for me in the British military firearms field (... not that I am terribly good to start with, mind you ...) I have no problem sharing my experiences and methods ... I will turn 70 this fall, so gotta pass on the lore before it is too late!