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Impact of barrel length on muzzle velocity
It has often been debated how barrel length impacts projectile velocity at the muzzle. The general principle is clear: the longer the barrel, the higher the velocity and the kinetic energy. The pressure created by the powder explosion accelerates the projectile in the barrel. The longer the barrel, the more time and distance is available to accelerate the projectile and, hence, the muzzle velocity is higher with increasing barrel length.
While the general principle is clear, we took a more scientific approach to determine this relationship in greater detail: We simulated the muzzle velocity for changing barrel length for two calibers (.308 Winchester and .300 Winchester Magnum) and the 50 most common propellants respectively. We then put the muzzle velocity (Vo) at 600mm / 23.6 barrel length to 100% and indexed the other numbers accordingly to this reference. Finally, we aggregated the values for all propellants for each caliber by taking the average. The results are as follows:
If you shorten the barrel length of a .308 Win from 600mm / 23.6 to 300mm / 11.8, your muzzle velocity reduces by 25% to 75%.
If you shorten the barrel length of a .300 Win Mag. from 600mm / 23.6 to 300mm / 11.8, your muzzle velocity reduces by 32% to 68%.
The results are different because the must suitable powders for a .308 Win are faster burning than the most common powders for a .300 Win Mag. Hence, the accelerate the projectile faster.
With the increasing use of silencers, barrel lengths vary significantly more. Our load data therefore indicates the relevant ballistic information for different barrel lengths.