M1903 Springfield isn’t used today but it was in service for 60 years.
Colt M1911 .45 pistol, which was used by the U.S. military from the 1911 until 1986: 75 years.
The Browning M1919 Machine Gun, still very much in use today: 102 years.
M2 .50 caliber machine gun. Ma Deuce. Introduced in 1933, the M2 is an old workhorse that isn’t going out to pasture anytime soon: 88 years
M60 was introduced in 1957, it was perhaps the best Cold War era general-purpose machine gun: 64 years
M1903 Springfield is the first rifle bigger than a .22 that I ever shot. I was about 13 at the time. I remember not liking the recoil very much. I was much skinnier than I am today. I wished I had one. They used to be very cheap to buy and now they are costly.