overloading a 45/100 cartridge using black powder

[Kevinjoe]

Can you overload a 45/70 or 45/100 cartridge using black powder? If I were to just fill the cases with 2F or 3F and compress it with the bullet....could I get an over pressure situation?

[Bent Ramrod]

In a word, no. Unless, of course your gun is damaged, decrepit or otherwise marginal for the caliber. What are you shooting?

The Sharps Co. designated their cartridges by caliber and length of shell, rather than by a nominal powder charge, because customers would load whatever black powder charges that could be gotten into the case. A .45-2.1” (AKA .45-70 by other manufacturers) could be loaded with 80gr or more of black powder; a .45-2.6” could hold 105-110 grains, although it was called a .45-100. Later, the 2.6” length was dropped for a 2.4” long shell, which would still hold 100gr of powder, although Winchester and other manufacturers called their versions .45-90.

You are likely to get a faster burn with 3F in a big case, which might increase recoil and raise point of impact, but it shouldn’t raise pressures seriously above the typical 23,000 lb that black powder generates.

Substitutes are something else again. There, you’re on your own.

[Jeff Michel]

Welcome to the forum. Bent Ramrod is correct, but I would add that you shouldn't compress your load with the bullet. It will likely expand enough that it will not chamber.

[Brimstone]

Yeah don't use the bullet as a compression plug as you'll mangle it, that's what the Buffalo Arms compression plug is for.

Also, fears of overpressure and blown up guns are mostly the domain of smokeless loaders (I hesitate to say exclusively) and why I do not talk reloading black powder cartridges at shooting ranges.
Card wads, compressed powder, grease cookies? Oh my.