Most of us, when starting out, buy whatever black powder is locally
available, not knowing much about powder, granulation, and some of the
other fine points. For those folks, it is worth understanding powder
granulation, and what each is used for.
Black Powder is normally graded as Fg
(coarse grain), FFg (medium grain) and FFFg (fine grain). The finer the
grain of the powder, the faster it will burn, and the higher the peak
pressures tend to be. There are other powder grades used, which are
typically for more specialized uses, but these three are the most
commonly used grades.
Large bore rifles (typically larger than .62 caliber) will use larger charges of Fg. Medium bore rifles of between .45 and .62 caliber will use moderate charges of FFg. Smaller rifles and most pistols will use relatively light charges of FFFg. Specific charges are not given here, because that is what you determine while working toward a good group. A very good starting point for determining what charge size to use is to use 1.5 grains of powder per point of caliber for Fg and FFg loads. It is safer to begin FFFg loads at 1 grain per point of caliber. Here are a couple of examples:
The final charge may vary significantly from your starting point. Some
find that a larger charge provides the best accuracy, and some find
that a smaller charge will be most accurate. If all you will do with
your rifle is shoot targets, the minimum charge you can use is whatever
groups best. If, however, you will use the rifle for hunting, it is
imperative that whatever charge you use has sufficient energy to
humanely dispatch your prey.
Each rifle may have it's own preference for the powder that provides the best group, and in some rifles one powder will shoot significantly cleaner than others. All rifles are definitely not alike in these regards. It may be benficial to experiment with several different powders, if you have more than one brand and granularity to choose from. There are a variety of powders available from a number of manufacturers. In some areas, there is more variety available than in others. You may find that using a finer or coarser grain powder in your rifle results in a better group. Just remember that if you change granularity, you must change the size of the load. To produce equivalent energy, finer grain powder requires smaller charges, and coarser grain powder requires larger charges.Within reason, it is good to experiment with some of these variables to determine the very best combination for your specific rifle. It is imperative that the shooter understand the safety limits of powder charges. Many shooters have loaded a ball without first loading the powder charge, and that is not a huge problem, provided one can remove the nipple on a percussion gun and pour some powder into the chamber through the snail, or pour some powder through the touch hole on a flintlock to remove the offending ball, and fire the ball out with a very small charge. One may have to attempt this a couple of times to extract the ball, but there won't be any damage, except to your pride. The other end of the spectrum isn't quite as forgiving.
Overcharging a rifle can result in damage to the rifle, injury to the shooter and others standing nearby, and even death if the charge is too great. It is extremely important that one never make large changes in the size of a charge, at least when increasing the charge size. It is doubly important that one pay extremely close attention to the loading procedure when charges in the upper end of the scale are being used. A double charge could be catastrophic!
Recognizing the signs of overcharge is very important, so a small
segment regarding this is included here. When one is firing a flintlock
rifle, the open vent provides a safety factor that isn't available to
percussion shooters. In any case, the close observation of indicators
is a wise idea.
The first indication of overcharge is that unburned powder is being ejected from the muzzle. This can be detected by firing over a white sheet or simiilar large cloth, and looking for black specks of unburned powder. A few grains of powder will almost always be ejected, but any significant amount of unburned powder being ejected means that, at the very least, you are wasting powder.
If one is shooting a percussion rifle (or pistol for that matter), a
second indication of overcharge is the percussion cap being blown off
the nipple, or the hammer being blown back to half-cock. These are sure
indications of an overcharge, and one should reduce the charge by at
least 10%, and be more careful if the charge is increased again. Once
you know what charge is sufficient to blow the percussion cap off, you
know what the practical limit for that power, patch and ball