Original sentence: It was adopted by the US Army in 1957 and served for almost 35 years, not without substantial criticism by troops who used it in the field.It was gradually replaced in the late 20th Century by the M240 machine gun (a licensed copy of the FN MAG), which was finally adopted by the US military in 1991.The M60 machine gun began development in the late 1940s and borrowed strongly from German designs such as the MG42 and FG42, combining the stamped sheet metal construction and belt feed mechanism of the former with the often unreliable and exceedingly complex gas-actuated operating system of the latter
Edited sentence: It was adopted by the US Army in 1957 and served for almost 35 years, hated the whole time by almost everyone who had to use it.It was gradually replaced in the late 20th Century by the M240 machine gun (a licensed copy of the FN MAG), which was finally adopted by the US military in 1991, more than three decades after the M60's glaring deficiencies were well-known to everyone who cared.The M60 machine gun began development in the late 1940s and borrowed strongly from German designs such as the MG42 and FG42, combining the stamped sheet metal construction and belt feed mechanism of the former with the finicky, unreliable, fragile, excessively complex gas piston operating system of the latter