August 24th 2021
What you need to know about powder grain shapes
POWDER GRAIN SHAPES — What You Need To Know
The shape of powder grains can have a significant impact on the performance of powder charges. This includes both pressure and velocity. There are many powder shapes, including flake, ball and extruded (or “stick”) (both solid- and perforated).
How does powder grain shape influence pressure and muzzle velocity? In general, powder that burns slowly at low maximum pressure achieves a desired muzzle velocity. The maximum pressure moves towards and towards the muzzle as the grain size increases. This also increases muzzle blast. The amount of powder or loading density can adjust the muzzle velocity and pressure, i.e. The relationship between the powder mass (in grams) and the volume that is available to it. Maximum pressure increases as the loading density rises.
All Vihtavuori’s reloading powders have a cylindrical, single-perforated extruded stick shape. The composition, the size of the grains, the thickness of the cylinder walls, the coating, and the composition all affect the differences in the powders’ burning rates. Multi-perforated grains can be found in cylinder extruded powders. The 7- and 19 perforated varieties are the most popular. Multi-perforated powder grains are naturally larger than those with one perforation and are often used for large caliber ammunition.
Flake, sphere and ball are other types of powder grains. The ball grains are used in automatic firearms, but also in rifles or handguns. Because it is not pressed into a cylindrical shape, the ball grain is more affordable to produce. Shotgun loadings are often made from flakes-shaped grains.
In gunpowder terminology, web thickness refers to the minimum distance the combustion zones can travel within the powder grains without coming across each other. This distance is defined as the distance between the combustion zones in spherical powders and the powder grain. In flake powder, it is the diameter of a flake. In multi-perforated extruded powders, it is the minimum distance (i.e. Wall thickness between the perforations.
The surface area of the grain that is available for burning at any pressure level determines the burning rate of powder made of grains. A form function describes the change in the surface area of the grain that is burned during combustion. The form function is progressive if the surface area increases. If the form function decreases, it is called degressive. We call it neutral behavior if the flame area remains constant throughout combustion.
Perforated, cylindrical powders are progressive. The burning rate increases with increasing surface area, while the pressure builds up slowly, increasing until it reaches its maximum and then collapsing. Degressive flakes and ball grains have a maximum powder surface area and pressure at ignition. This pressure decreases as the combustion progresses.
This article was originally published on the Vihtavuori Website.
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Tags: Alliant. Burn Rate. Flake Powder. Gunpowder. Hodgdon. N133, N150. Perforated Powder. Propellant. Stick Powder. Vihtavuori. VV Powder.
