About black powders and how it works.
What makes powder burn fast, is surface area.
In short, this is why 1F has larger "chunks" then 2F, which is larger than 3F, etc etc,
In the olden days of lore, they had granular powder, that was the size of your thumb, for lobbing the huge cannon balls without bursting the cannons themselves. The huge granules burned slow enough (because of surface area), they were able to produce the force slow enough without reaching breaching pressure of the cannons before the ball left the barrel.
Lets take a 1 inch square cube. It has six sides with a total area of 6 square inches of surface burn. (we will call that 1F)
Take that same cube and cut it in half, and we have two rectangles, each with a surface area of 4 square inches. We still have the exact same amount of powder, but we now have 8 square inches total of surface area to burn, instead of 6.
Take those same two rectangles and cut them in half. That means we have 4 cubes with a total of 3 square inches each, making a total of 12 square inches of surface burning.
As you see, we have the exact same amount of powder (by weight) and (by volume), but the only difference is, we have exposed more surface area to burn, in fact twice as much surface area quite easily. This means a much MUCH faster burn. . .twice as fast burn as the solid one inch cube.
Now, if you take your 4 pieces of powder and pack it all tight back into a little bundled up wad, your surface area is now restricted down from 12 square inches to maybe 8 or 10. This slows down the burn.
Take a look at firecracker powder. . .It will ALWAYS be in the finest powder form there is, for the fastest ignition, and the most surface area to ignite and follow through with that ignition of the whole thing. It is usually called flash powder. Reason: almost instantaneous ignition.
Lets take a look at our modern day powders. What is the fast powder used for? For Pistols and extremely small caliburs in which the projectile is VERY light, and will be forced out of the barrel exceptionally quick,before barrel breaching pressure is reached. For the most part, that usually means 45 cal or less. . .and if you push it to 50 cal, manufacturers usually ask you to use about 10 to 15 percent less 3F, than what you would use with 2F. Granted, there are some manufacturers that say it is ok to use 3F in their 50 cal, and sometimes their 54 cal. But they almost always say use less 3F than 2F. (3F is more surface area, meaning faster burn, meaning higher pressure before projectile leaves the gun).
What is slow powder used for? Higher cal guns, where the projectiles are heavier, and where the powder needs to burn slower, so that the breaching pressure is not reached before the projectile leaves the gun.
Now, the question becomes: How do you control the rate of burn of the powder you are using?
It is quite simple. . .It is all about surface area. You compact that powder down, you remove the surface area being exposed to the primary flame, and slow down the burn! And for this reason, the exact opposite exists. . .if you have a whole lot of air all around, and containment, you have a perfect bomb. What causes a bomb? Try loading a muzzleloader and have your projectile 6 or 8 inches away from your powder. You have the perfect bomb. Pure air, free and clear of any obstruction. . .loose powder that has *all* of its surface area exposed to be burned, and nothing to inhibit the burn. This is the exact reason why a person should always take his ram rod and shove it down the barrel after any kind of questionable Poof, that may let him believe the projectile never left the gun. In doing so, he has confirmed the project has either left, or has traveled up his barrel, making it a unsafe pipe bomb.
Now, lets talk about flintlocks and how the flame travels, as well as how it ignites.
What we are looking for, is "Lock-time". We want the lock time to be as fast as possible. Since flint locks do not use any kind of primary fire, like a "CAP", or a "Primer", the flame must migrate grain by grain through the pan, into the chamber, and through the main charge. (A percussion forces its fire into the main charge, as well as a primer).
We all know that surface area is the way a powder will burn, and the more surface area you have exposed, the faster it will burn. If you take that powder and compress it, you are removing the surface area, causing the powder to burn slower. (because it has less surface area burning, and it must migrate through a more solid object, similar to a fire migrating through a tunnel of 4F and a tunnel of 1F. ) It takes much longer to migrate through powder that is packed, than loose.
Now, how should we prime our pan? With LOOSE powder, spread out, and not compacted in any way. We want maximum surface area to ignite and spread to its fullest.
Now how do we want our main charge??? AS LOOSE as POSSIBLE but having the projectile ON the powder without forcing the powder to be "crunched","crushed", or "packed" into a size that is reducing the size of the powder more than what your "volume" measurement was when you started. This insures plenty of air pockets, air circulation, and allows the flame to migrate through these pockets quite quickly and rapidly, causing your lock time to be extremely fast.
You start "crunching down" your main charge, you will probably start getting those "FSSSST" bang! or something very similar. You stop crunching down, allow the powder and air to do its job, your shots will start ending up being a extremely fast click-bang, with the lock time being extremely short.
Just a little info on powders and how they work. . . (ignoring that as pressure increases, powder burns faster)
Dwayne