4 bore

4 bore
Portrait of Frederick Courteney Selous with his 4 bore single-shot smoothbore gun and African hunting regalia, 1876.
Type	Rifle or Smoothbore, Heavy Game
Place of origin	British Empire
Specifications
Bullet diameter	1.052 in (26.7 mm)
Case length	4 in (100 mm)

Four bore or 4 bore is an almost obsolete black powder caliber of the 19th century, used for the hunting of large and potentially dangerous game animals. The specifications place this caliber between the larger two bore and the lesser six bore. This caliber was the quintessential elephant gun caliber of the black powder safari rifles.

The name derives out of an old English practice of bore measurements in gunmaking, meaning a perfectly round pure lead ball that exactly fits the bore of the weapon would weigh 1/4 lb—that is, 0.25 lb (0.11 kg) (see gauge). The 4 bore was made to fire roundballs of 1/4 pound lead, or approximately 1750 grains (1750 gr.) and approximately 1-inch (25 mm) calibre (more precisely, 1.053-inch (26.7 mm), when shooting pure lead bullets). This varied greatly as in muzzle loader days shotgun gauges were custom made and often differed from the actual bore measurements. Commonly, 4 gauges were closer to .935–.955 calibre, pertaining to a 1400 gr. alloyed lead ball and closer to 5 gauge.

As European settlers found early on, their regular muskets were inadequate against dangerous African game. Early gun adaptations were to use smoothbore shotguns with extra long barrels and round balls. By the mid-19th century, 12, 10, 8 and 4 bore muskets had been strengthened and bulked up for much larger charges. Shooting dangerous game was still at this stage as much about being able to gallop away on horseback to reload and fire again, repeating this process up to 30 times when after an African elephant.

The first 4 bores were probably single barrel muzzleloaders converted from British fowling pieces that were, in essence, slug guns. Loads (bullet weights and gunpowder loads) varied greatly. As the weight and strength increased, gunpowder loads went from 8 drams (0.5 oz) to a full ounce (16 drams), or more, of powder. The advent of rifling after about 1860 allowed longer conical projectiles to be stabilised, and, aside from accuracy, these provided even greater weight and penetration, with some hardened lead or steel bullets weighing as much as 2000 grains. The 4 bore was also occasionally used for shooting exploding projectiles. Although 4-bore firearms were commonly referred to as "rifles", smoothbore version of the weapon were actually more popular, and continued to be so throughout the era of four bore usage. Since dangerous game was shot at ranges under 40 yards, a smoothbore was sufficiently accurate, while at the same time providing higher velocities and lower recoil, and needing less cleaning. The prominent British gunmaker W. W. Greener even recommended against rifled firearms above the bore size of eight, with the four bores that he continued producing from then on being exclusively smoothbores. The smoothbore also, at least until the advent of breechloading, could be reloaded faster.