(from Red Coat and Brown Bess
"Many authorities in the United Kingdom felt that the length of the Long Land barrel was too long and unneccessary. Experiments had shown that a barrel length reduction had no effect on range, A shorter barrel would mean a weight reduction, not to mention ease in handling. Dragoons had used the Short Land Pattern musket, one with a 42 inch barrel for years...In June of 1768 the Ordnance decided upon a new pattern musket for land service. It was, in effect, a modified version of the Dragoon short land...Although generally referred to as the Second Model Brown Bess, the musket's actual contemporary nomenclature was the Short Land Service Musket (New Pattern)."
Production commenced in 1769.
"Very limited production of the Long Land continued for a few years, perhaps only on special order...manufacture of Long Land barrels did not cease until 1790. The actual date when the new pattern muskets were first issued to the regiments can only be guessed at. However, the newly-raised Frasier's Highlanders were equipped with them in 1775. The vast majority of muskets examined, which are regimentally marked and can be attributed with reasonable accuracy to use by the British Army in North America during the American Revolution are of the short land pattern. Apparently, the Long Land Service musket was relegated for use by Provincial or Tory battalions that served in the war."
Red Coat and Brown Bess byAnthony D. Darling pub. Museum Restoration Service eighth printing 1987 quotes from pp.21 to 23