Range, Power, Penetration, Velocity of a Brown Bess – Roberts, Brown, Hammett and Kingston

Abstract
During the mid 18th century, the standard British Army issue weapon was the Brown Bess Musket. There are various accounts of the performance of this early form of firearm and its tactical deployment (e.g. Hanger 1816). Using a technical replica of the Brown Bess, range trials and computer modelling have been used to asses the weapon’s capabilities and likely performance. The research found the Brown Bess musket to be a lethal weapon at the ranges at which enemy was commonly engaged, so long as it was accurate enough to hit the target. A single shot fired at 150 yards could penetrate at least two soldiers, even if bone were hit. The armour of the day (shields of wood, leather and sometimes steel, and the layers of woollen clothing) was easily pierced by the shot. The shot was found to readily deform on impact with metal targets. The maximum range could extend to around 1200m, with 202m reached when fired horizontally.

The results of this experiment hinge on an assumption by the authors that the muzzle velocity of a Brown Bess was 1,500 feet per second. We don’t know for sure how powerful historical gunpowder was, or what the velocity of a musket ball was. But we have a reliable source. Benjamin Robins invented the ballistic pendulum in the early 18th century, and his book New Principles of Gunnery (1742) contains the results of his experiments. Robins calculated the velocity of a 1/12th pound ball fired from a .75 caliber musket (the same size as a Brown Bess). His results ranged between 1,600 and 1,700 feet per second. The authors’ assumed velocity of 1,500fps is therefore conservative.

Now here’s the most interesting part to me: the authors weren’t able to achieve a 1,500fps muzzle velocity with any of the three modern powders they tested. This flies in the face of the common assumption that modern gunpowder is more powerful than historical powder. Modern powder may be more chemically pure, but the power of gunpowder is linked to the size of the powder grains. Very fine grains burn fast and larger grains burn more slowly. The optimal grain size for maximum power depend on the size and strength of the barrel. The authors found that by mixing  two types of modern powder together, the musket achieved a higher muzzle velocity. They posit that this is because each powder has its own pressure curve. Combing the powder combined the pressure curves, increasing the time that the bullet was under maximum pressure. Perhaps the impurities and inconsistent grain size in historical powders made them stronger, not weaker.

Like in the Graz tests, the maximum range was calculated mathematically, not actually tested.

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