reloading part 2 - Smokeless powder
Part 2 –smokless powder
Most metallic cartridges loaded (or reloaded) today are charged with smokeless powder. Smokeless powder has evolved into our current crop of high quality, high energy propellants that allow one to handload cartridges as small as .25 ACP to as large as .50 BMG (or larger).
Smokeless powder is technically not explosive. It burns at a controlled rate rather than detonating all at once.
Smokeless powder is generally categorized as either single base or double base.
Single base smokeless powder is made with Nitrocellulose. Double base smokeless powder is made of Nitrocellulose and Nitroglycerin. There is triple base smokeless powder that adds Nitroguanidine. Most triple base powders are used in large bore artillery shells (cannons).
Smokeless powder is further differentiated by the shape and size of the individual kernels. Spherical (ball), flattened sphere, extruded and flake. Each formulation has its own characteristics including burn rate and ease of metering.
There are relative burn rate tables available that arrange the different brands by the speed at which they burn “relative” to the others. These tables should NEVER be used to develop a load. Just because IMR 4350, H-4350 and AA4350 appear one after the other on this chart does not mean that the powders are interchangeable. Each powder has its own characteristics that affect how it actually performs when ignited.
Spherical (ball) powders are desirable as they tend to meter smoothly in loading machine powder measures. Ball powders generally burn cooler than other powders but leave more sooty residue. Most military small arms ammunition is loaded with ball powder to reduce the amount of heat build up in a fully automatic weapon.
At the other end of the spectrum are the extruded powders. These appear as sticks of various lengths and thicknesses. They tend to be high energy powders that are capable of yielding higher velocities than other types of powders.
Load data published by the powder manufacturers, the bullet makers and the reloading machine makers is the basic guide in load development. Each batch or lot number of a particular powder will vary from the others. Published maximum loads are to be approached with extreme caution. Generally one either starts at or near the bottom of the charge weight recommendations and gradually loads test ammunition with heavier charges until the desired results are reached. Normally these increments are ½ to 1 grain but may be smaller depending on the desired results
When a different batch (lot number) of a given powder is purchased. The previous data should be reduced by 10% and worked up again. To avoid having to repeat this trial and error process, many loaders will purchases several pounds (or one larger keg) of one lot number.
Extruded powders have a propensity to “bridge” or get stuck in the powder measure resulting in inconsistent charge weights. Loaders who prefer these powders often use a “trickler” that dispenses very small amounts of powder into a pan until the desired weight is reached.
Smokeless powder charges are generally measured in grains. This is a measure equal to 1/7000th of a pound. The individual kernels of powder are sometimes referred to as grains but this is not a weight reference. A 50 gr. charge of powder is not 50 kernels and must be weighed.
Loading density is a term one might see or hear. This refers to amount of volume in the case the powder charge takes up. Most smokeless powders work best when 70-100% of the available space is filled with powder. When the case is filled to 100% capacity it is considered to be a compressed load. That is to say the bullet will press the powder charge down when it is seated. Some powder/cartridge combinations will require a compressed load to yield maximum results. In some cartridges with some powders, a compressed load will be VERY dangerous.
On the other hand, some loadings will fill very little of the available space. The most common powder used in very light loadings is Bullseye. Very light charges of Bullseye were the mainstay for revolver competition for many years. When these very light charges are used there is sometimes a problem with detonation. Smokeless powder generally burns progressively. The primer sets off the part of the powder charge nearest the base which in turn sets the rest of the powder alight as the flame reaches it. When a very small charge is used, the powder can lay along the side of the case instead of against the flash hole. The primer sends the spark/flame across the charge rather than through it. There have been reports of catastrophic results linked to this phenomenon.
Then there is the odd ball powder, Winchester 748. This is a very high energy powder designed for magnum handgun ammunition. It has unique characteristics in that it will yield very high velocities at lowered pressures. 748 should ONLY be used at the recommended load weights (never reduced). Reduced charges of 748 can yield wild pressures that can become dangerous.