What is the OLDEST model weapon that you used in the Military?

While on a patrol with a Vietnamese Ranger unit I carried an M3 Greasegun.

Add the M3A1 Grease Gun when I was stationed in Germany from 86-89. What a fun little weapon! My 1911 was WW2 issue...actually had to aim about 6" to the right to hit the target COM. We just considered it a challenge...still qualified Expert Pistol

.38 revolver.

A M3A1 Grease gun, I used and fired in Germany while stationed at Robert Lee Casern (Barracks), 1977-78 was a fun 45 ACP shooter.

The colt 1911 was used by me once in Vietnam to qualify. I hit the South China Sea every time!
In basic training I hauled around the M-14 almost all the time and was used to qualify. The M-16 was introduced during the last week of basic training and while in Da Nang the M-16 was removed from locker and put into the Armory to never be seen again.

1911 ACP 45 semiautomatic,
1903 Springfield
M-16
(Now the fun)… 5”38cal Navy , 5” 54 cal Navy.

Yes, the M1911A1 .45 was my standard service sidearm (worn with a shoulder holster). The Beretta (which I disliked) was fielded as its replacement the year I left service. I also used the .50 Cal M2 machine-gun on occasion, but not on a tank; my tank commander's cupola was equipped with a .50 Cal M85 machine gun--which was an M2 redesigned to feed from the right (and a truly great way to fudge up a weapon that was superb in its original left-side M2 feed configuration). I also qualified on the M16 (M4s didn't yet exist)--which was a ridiculous requirement because the length of the M16 was too much for easy maneuver inside a tank, so none of my armor crewmen ever carried them. The M60 machine gun, of course, we also fired at the range, and the Belgian made M240 MG (this was the coaxial weapon in the M60A1/A3 tank turret beside the 105mm M68 main gun cannon) during tank gunnery exercises--and both the M60 and M240 borrowed the design concepts from the German WWII MG-42 MG (which the Germans still use today in NATO caliber as the MG-3) But, each of those weapons was contemporary with my service period, as was the Vulcan 20mm Gatling gun ADA system, which I fortunately also had a chance to fire (a blast to use on old autos downrange)! But the OLDEST model weapon that I ever used/fired during my Army service was the WWII vintage .45 CAL M3 "Grease gun"--which were actually still available as personal weapons for tank crews owing to their convenient short length (though they were never actually issued)--we did, however, enjoy firing them at the range!

In my personal life I own and fire a WWII vintage Springfield .30-06 M1 Garand rifle and a .30 Cal (long) M1 Carbine (by Inland), an M1911 .45 Cal automatic manufactured in 1917 (i.e., BEFORE the M1911A1 model came out), and a 1915 P-08 Luger (9mm) made by Deutsche Waffen und Munitionsfabrik ("DWM") as well as a WWII Walther-made P-38 (9mm).

I'm thinking a .38 Model 10 Smith N Wesson, the .50 M2 was a gimme. One place I was at, the M16 was a Colt without a chrome lined barrel, surplus from early Vietnam I recon had to be like 1965-66... not the later M16a1... the 81 tubes I shot...IDK... Clark in the PI and at Osan ROK were finned types... probably like the 1970's. The M60's were from the 50's... A Mark 19, 40 mm with a 12 round detachable mag was an early ass version late 1960's maybe.

The ones now don't even look the same.

The USAF Armory dudes locked up all the 1911's, so were the M79 and the M1/2 carbines. I don't recall any M1 Garand's on site in my day.

In no order:
M3 grease gun
1911
M60A4 105 round
M2 dang thing is frigging heavy
Tank mounted MG's
LAW
Hand grenade

M1 carbine, in 1971 when you transferred from base to base in the Air Force we had to qualify on the rifle. At this time there was a shortage of M-16 and we qualified on the M1 which I had never seen or fired before that time.