I’m looking for a weapon which was manufactured a long time ago and is still used on regular basis. Replicas and mere museum exhibits which happen to be still functional don’t count.
To give an example, in the German military, the unit which performs military honors for visiting dignitaries and the like still uses on a daily basis Karabiner 98k rifles which were manufactured in the 1930s and 40s.
The knife.
The wooden club.
Rocks. 
The U.S. Army Drill Team uses 1903 Springfields.
This is all extraordinarily witty and humorous, but it is not what the question was about. So for instance, a knife would only qualify if:
(a) the specific knife was produced in, lets say, 1850 and
(b) it is still being used as a weapon
The canons on Edinburgh castle are still fired each day.
Unless that German military unit would use those Karabiners in combat as opposed to ceremonially, your own example violates condition (b).
The one o’clock gun is a modern artillery piece though. The castle has the bombard Mons Meg, which dates from the mid-fifteenth century, but it hasn’t been fired since 1680.
This. AIU the OP, the question is what is the oldest weapon still officially being used as a weapon.
How about if we start with the Colt Model 1911 and variants? Officially adopted in 1911, I believe some USMC units are using a variant today. I heard that many M1911-A1s made during WWII were being issued in the 1980s.
Does the German military really still use a gun made in the 1930s and 40s? Does it have little decorative swastikas on it?
No they aren’t - the one o’clock gun is an ordinary field gun (click on the bit that says “Explore more detail”).
http://www.edinburghcastle.gov.uk/explore-the-castle/highlights/castlehighlights.aspx?start=6
Does any countries military police still use wooden night sticks? I’ve seen recent footage of Indian soldiers breaking riots in Kashmir with long batons. But these could have been an old design rather than old weapons.
The Gurkhas still carry kukhris. But again its an old design.
Yes, some of the 98k rifles indeed still had swastikas engraved and this caused a minor scandal in the late 1990s, IIRC, when somebody took a closer look.
Fists of Fury! :eek:
Fair point. Indeed, they don’t use these rifles for combat.
I am interested in ancient equipment, in this case: weapons, which are still used and relied upon in modern times. One could say that a rifle on occasion was and still is used to strike an opponent. In this sense, the rifle is still being used as a weapon.
What does it mean for it to still be used as a weapon?
Someone could feasibly stab someone with an ancient sword/batter someone with an ancient club that hasn’t degraded too much. Is that ‘using it as a weapon’? Or is this more to do with it still officially being in service of some military organisation somewhere?
Israeli police volunteers are still issued M-1 carbines, manufactured in the 1940’s.
Sweet little firearm. I have two, and they’re a lot of fun. I’d rather have something else if my life depended on a gun, but for recreational use they’re very nice.
M2 BMG .50 Cal Machine gun. Entered service in 1919.