All types of smokeless powder fall under the category of “progressive burning powders.” As opposed to black powder gunpowder, which combusts all at once, progressive burning powders burn grain by grain. The time it takes for this powder to burn through varies; powder burn rate refers to the time it takes for the smokeless powder to ignite.
Powder burn rate is a somewhat complicated measurement that many shooters overlook. One reason burn rate is often complicated for beginners is that there is no universal measurement; rather, it is used to compare powders against each other. Regardless, if you are looking to maximize your round’s performance and ballistic profile, it is worth your time to understand powder burn rate and how it affects a round.
There is no “best” burn rate – the ideal burn rate for your smokeless powder will depend on how you plan to use it. In general, faster-burning powders are used for lighter bullets and shorter barrels, while slower-burning powders are used for heavier bullets and longer barrels.
Burn rate often becomes a consideration when loading magnum rounds. Since magnum rounds need to generate more power than non-magnum rounds, a slower-burning powder is usually used. With a slower burn rate, the powder will provide peak pressure for a longer time, delivering the extra power necessary. It is for this reason that slower-burning powders are also used for heavier bullets, which need a longer period of peak pressure to provide the necessary level of velocity and power.
A powder’s burn rate determines the relative speed and pressure at which the round moves from stationary (in the mouth of the cartridge) into the lead cone at the rear of the barrel’s rifling.
If a powder has a faster burn rate, it will take less time for the round to reach chamber pressure. This has an effect on muzzle velocity: generally, fast-burning powders are used in loads with the highest muzzle velocities.
While a high burn rate correlates with a high muzzle velocity, it also tends to reduce accuracy. As a result, shooters firing heavy rounds that depend on extreme accuracy tend to utilize slower-burning powders. Conversely, shooters who use lighter rounds and prioritize muzzle velocity over pinpoint accuracy will tend to use faster-burning powder.
One of the main considerations when considering the burn rate of different reloading powders is the type of firearm that will be used.
The biggest consideration when choosing a smokeless powder for a handgun is the significantly reduced barrel length. Since handguns need to give off as much energy as possible in the shortest possible distance, powders with fast burn rates are typically the best option. One notable exception is If the pistol fires a magnum round: a powder with a medium burn rate may be optimal in this case.
There are a wide variety of burn rates that are suitable for shotguns, though the best will depend on the type of shot. Heavier shots, like slugs or buckshot, require a slower burn rate, as heavier rounds will need more time to fully accelerate. On the other hand, lighter shots (such as birdshot) respond best to powders with higher burn rates.
Like pistols, the main consideration for choosing a burn rate for rifle rounds is the barrel’s length. Since the round is in the (considerably longer) barrel for a greater distance, a slow-burning powder is required to deliver the necessary amount of pressure for a longer duration of time.
Using a smokeless powder with an incorrect burn rate can be dangerous. For example, if you use a fast-burning powder with a heavier round, it may cause excessive pressure and pose a danger to the shooter. In contrast, using a slow-burning powder with a light round may not provide sufficient power.