There are so many similarities between the original Colt M1911 and the Colt 1991. In fact, the Colt 1991 is related to the original Colt M1911. The original version of the recoil spring remains from the original M1911 design as well as the long trigger and flat mainspring housing. So what’s different? Upgraded high profile white dot sights and a more modern lowered ejection port for reliability.