Hi tenngun. I don't have a 45 cal ML, only 50's. And I do have 2 45/70's and do quite a bit of loading for both of them. But I did notice that when pushing projectiles of the same weight, even in a 50 ML to 45/70 comparison [I know, that's a sin.], the data and my own experience says that velocities are quite comparable. A 50 roundball weighs close to 180 grains so, I am guessing that a 45 rb weighs about 150/160. Of course, that in no way compares to the standard 405, 45/70 grain payload but if you loaded a 45/70 w a 150/160 grain pill [admittedly very impractical], I would think the velocity would comp w a 45 ML prb if both used the same volume of powder. The data I have seen for a 50 hdy Great Plains, 385 bullet shows velocities quite similar to the ones I get w my 45/70's using projectiles of similar weight and 70 grains.
So, even though heretical for many, the comparisons can be useful when they are made apples to apples. [loads and bullet weights] It should be kept in mind that the 1st brass cartridge development was done by people who, previously, only had ML experience and they were making comparisons and predictions based on the physics of black powder and lead. While details in difference of design cause variations that have to be taken into account, there is no magic wall separating the principles involved in this. If the OP erred, it was in not specifying equal bullet weights per charge. Open to criticism here. Maybe I am missing something.
As to the OP's question on charges, even the 45/70 405 was found wanting by many and shortly, along came every imaginable variable of charge and bullet weight in .45 up to [and probably past] 120 grains of black. Of course, the larger variants had diminishing returns and, overall and in time, the 45/70 won out while some variants [90, 110, 120] still hang on to this day. I think, even in the huge variants, it was quite likely that, in the 1800's more 45/70 cases were fired in them than the cartridge the rifles were chambered for. [availability] And I think his basic thrust about huge charges of black powder for ML's [and even substitutes] is mostly warranted. It seems that somewhere around 70 grains or so there is a sweet spot for accuracy in these rifles. While a bit more power never hurts, accuracy kills. But some do find the accurate medicine they want with bigger charges and they should not have to justify that preference. SW
