Make no mistake about it, Black Powder or Pyrodex are the only propellant powders that are safe to use in a muzzleloading firearm. Oh, you will hear, or possibly read, advice to the contrary but don't follow it for you will never hear such advice from a competent source.
The reason for using a low yield powder such as Black Powder or Pyrodex is quite basic and it is related to firearm design. When used as a propellant, Black Powder or Pyrodex generates a relatively low breech pressure. Muzzleloading firearms, even those with modern steel barrels, are not designed to withstand the high pressures produced by a Smokeless Powder charge. Think about it for a minute and you will understand why. The ignition hole in a muzzleloading firearm is a direct port into the combustion chamber. This port is sealed only by the thin foil of a cap and weight of the hammer in the cap lock model. In the flint lock design this port is not sealed at all. The high pressure of a Smokeless Powder charge would destroy this ignition system and the gun itself.
To avoid any misunderstanding on the part of the reader let us explain further why Smokeless Powder cannot be used in a muzzleloader in any quantity. People who become interested in muzzleloading tend to research and to seek out some of the early journals which describe loading implements, components and powders of yesterday. Reading these old books can be pleasurable. Never assume, however, that obsolete printed material has a safe application in today's world.
In the early days of the breech loader there were powders manufactured which were called "Bulk Smokeless". These powders were measured by the volume and used interchangeably with Black Powder in early cartridge firearms. Even in their time these powders were never used in muzzleloading firearms.
Early "Bulk Smokeless" powders are not available today and, even if they were, their erratic performance (extreme variations in pressure) would not meet current industry standards. By modern standards, such early bulk powders were unsafe, even in the days of their use. The same type of misinformation exists concerning "duplex loads" or the mixing of Smokeless Powder with quantities of Black Powder. This practice was popular in the days of the early breech loaders. It was dangerous then and it is even more dangerous now for modern Smokeless Powders are far more complex in their composition.
All presently available Smokeless Powders are designed for use with metallic cartridges and shotshells in strong modern breech loading firearms. They should never be used in a muzzleloading firearm of any type. Some of these powders are "Black" in color making proper identification extremely important. It is the characteristic of Smokeless Powders to burn in a controlled manner within a given pressure range. Control of this pressure range requires the proper application of the powder to the specific purpose and in the quantities for which it was designed to be used.
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