From 1780-1781, Manton was first apprenticed to a gunmaker in Grantham, Newton. He worked under his elder brother John from 1781 onward. He produced around 100 weapons annually, including both cased duelling pistols and shotguns.
Tube lock
In the early-19th century, Manton invented the tube lock, an improvement over Alexander Forsyth's scent-bottle lock. Rather than storing a reserve of fulminate in a container, they now used single-use pellets or pills. The hammer of the gun was sharpened; when it fell, it crushed the tube/pellet, causing the fulminates to detonate. Although more reliable than Forsyth's design and adopted by many sportsmen during the Regency period, it was quickly overshadowed by the percussion cap, which was adopted by the armies of Britain, France, Russia, and America to replace the flintlock.
Artillery
The greater part of Manton's career was spent at loggerheads with the British Army. Manton managed to interest the army in purchasing a larger version of his wooden cup design to be used in rifled artillery. Manton worked tirelessly to improve cannon's firing accuracy. He created a new type of ammunition. First, the ammunition was loaded in a rifled cannon. Secondly, the cannonball was attached to the wooden cup that fitted into the rifled grooves of the cannon, which was in turn connected to a sack of gunpowder, thus eliminating the need for powder and shot to be loaded separately. The idea of fixing the powder behind the shot in a disposable cartridge is the basis for modern bullet design. It helped pave the way for breech-loading weaponry.
The army provided Manton a cannon and funding, and in return expected a greatly improved weapon. Manton's design was superior, although an argument over payment caused the army to declare it of little benefit. A row erupted over how Manton was to be paid; he believed the agreement was to be a £30,000 lump sum. The army argued that since they had already invested money into research and development, they did not want to pay such a huge amount of money for a design that had not been field tested. Manton patented his design, forcing the Army to deal. The army offered him one farthing for each shell they produced, but Manton refused this offer. Surprisingly for Manton, the army stood its ground. Manton was frightened that he had spent time and money developing a weapon that the army would not use. The Army rejected his offer, whereby the army could make the shells without paying royalties, while Manton would make the wooden cups. His design was more reliable than Forsyth's design and adopted by many sportsmen during the Regency period. After more than a decade of unsuccessful legal battles, Manton lost his vast fortunes and was declared bankrupt in 1826. His Oxford Street workshop was seized and his stock of guns bought by Joseph Lang, an aspiring gun dealer whose company would eventually become part of Atkin, Grant and Lang. Lang is credited with opening one of the first shooting schools in the premises adjoining the Royal Theatre Haymarket.
