76.2mm Shrapnel 

Russian 76.2mm shrapnel from 1905. The projectile was used during World War I and was fired using a wz.1902 field gun. The wz.1902 field gun was a Russian design from before World War I, partly based on the French 75mm wz.1897 gun. The cannon was still used during World War II, although the production of shrapnel, which is mainly discussed in this text, was ended with the end of World War I.

At the time of writing (Wednesday, October.04.2023), this is the oldest item in the collection and I don't think I will acquire something older anytime soon.
Update 22.02.2024: No is 2nd oldest item in my collection