Mr. Tinker:
It is hard to say for sure just how good the powders were back when black powder was gunpowder. The making of black powder is part science and part art, and much of the knowledge was lost when the world went to the new fangled imitation gunpowder.
I have read of anecdotal tests of remnant cans of old powder vs. modern, but I don't know if any such test would be conclusive, because any old powder would be, well, old. Without having been preserved in a properly controlled environment, what ever that may be, there is no way of knowing that the properties are the same as when the powder was young.
Personally, I don't think that the powder was necessarily much better back then, but there were a lot more choices and I suspect it would easier to obtain the optimum powder for a given application. There were musket powders and rifle powders and sporting powders and fowling powders and who knows what all. Loads for specific arms specified the brand and granulation of powder. Powders were produced regionally as well, and therefore likely optimized for the local climate. Atmospheric conditions, particularly relative humidity, do affect how black powder performs.
Perhaps the main reason it is difficult to achieve the velocities recorded in the past with a given cartridge today is that the cases are constructed differently. There is a lot more brass in a modern case and it simply will not hold as much powder.
But to answer your questions about currently available powders, there is no doubt that Swiss powder has more bang per a given volume or weight than Goex. The relatively new Goex Express is more powerful than standard Goex, but still not the equal of Swiss.
In the search for velocity I would not fear to use 3f in the smaller cases your mention such as the .410 and 28 gauge. I use Swiss 3f in certain .45-70 loads for the velocity increase, but this is in a falling block rifle. I personally would not be afraid of using it in an original double gun of .45 or less in good condition, but you have to follow your own head on that one. I have no personal experience with double rifles.
BP velocity depends on a number of factors, but to give you a vague idea of the difference in powders, in a .45-70 with a 500 grain bullet one could expect a 50 to 75 fps increase switching from Goex 2f to Swiss 1-1/2f. Similarly, there will be an increase in velocity of 40-50 fps from Swiss 1-1/2f to Swiss 3f.
As always, your mileage may vary...
Best of luck,
Glenn
