Howdy
The BATF classifies real Black Powder as an explosive. This means local regulations for storage, particularly in gun stores can be more onerous than with Smokeless powder, which is classified as a progressively burning propellant, not an explosive.
Black Powder substitutes are not classified as explosives, they fall under the same regulations as Smokeless powders, so storage regulations for the substitutes can be less onerous than with Real Black Powder.
That is one reason you are finding Triple Seven everywhere. It has always been that way.
As an example, there used to be a shop about an hour from me where I would buy real Black Powder, usually 3 pounds at a time. One day the clerk of the shop screwed up renewing their paperwork, and in order to renew their permission from the BATF to continue selling real Black Powder, they had to make several, expensive changes to the storage facility where they stored the BP. As a result, the shop stopped selling real Black Powder and from then on only sold the substitutes.
The first, and original Black Powder substitute was Pyrodex. Pyrodex was formulated to have the same energy as real Black Powder, volume wise But Pyrodex tends to be more corrosive than real Black Powder.
Just like with real Black Powder, if you are going to use Pyrodex in metallic cartridges, it is best to use bullets lubed with a soft, Black Powder compatible bullet lube such as SPG. Using standard, modern Smokeless bullet lube with real Black Powder or Pyrodex usually results in hard caked fouling in the bore that can ruin accuracy and be difficult to remove. Using a BP compatible bullet lube prevents this.
Triple Seven is made by Hodgdon. I have always heard 10% for how much more energetic Triple Seven is than real Black Powder, but 10% or 15%, Triple Seven is a bit more energetic. Unlike real Black Powder, which performs best with a little bit of compression, Triple Seven should not be compressed. When loaded into cartridges, just enough should be used so that it touches the base of the bullet. Just like with real Black Powder,do not allow any airspace between the powder and the projectile.
The other BP substitute that I am aware of is American Pioneer Powder (APP). The beauty of APP is it does not require a BP compatible bullet lube, it can be used in cartridges with regular Smokeless style bullet lube. A bunch of years ago I wanted to load some 38 S&W (not 38 Special) with BP but did not have any bullets for 38 S&W with BP compatible bullet lube (38 S&W bullets are slightly larger in diameter than 38 Special bullets.) So I loaded up some 38 S&W with some bullets with standard Smokeless bullet lube without any problems. It has been quite a while since I loaded those rounds, but I seem to recall I did not compress the powder, I seated the bullets at the top of the powder charge.
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One thing you are going to hear a lot about is "Grains Volume". There is no such thing. But the idea is the Substitutes, except Triple Seven, were formulated to have the same energy as an equivalent volume of Black Powder. So generally speaking, using a volumetric powder measure like this one, simply set the volume on it to be the same as you would for a charge of Black Powder and you will be good to go. If you look closely, the sliding dohicky on this powder measure is set for 30 grains. If I wanted a load of Pyrodex or APP the same as a charge of Black Powder, that is how I would set it.
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One last thing. I find it annoying when shooters refer to real Black Powder as the 'Holy Black'. There is nothing holy about Black Powder, it is simply an old fashioned propellant. Calling it the Holy Black just adds to the confusion about shooting real Black Powder.