Ammunition is extremely easy to find with a metal detector. Cartridges are large chunks of brass, which would make them obtrusive even if they were just spheres. But they are in fact sheet-metal cylinders closed at one end, which means that whatever orientation they have in the ground, there is usually two metal planes reflecting the detector’s signal. They shrill like mad.
Above is a pic of two cartridges I picked up at Sättuna today. The left-hand one is the most common type in Swedish farmland, used mainly to hunt large mammals, but also I believe in standard-issue army rifles of the 20th century. The right-hand one is something more unusual. I have only come across it at Sättuna. Look at the size! The two cartridges measure 55 by 12 and 99 by 20 millimetres respectively.
Sättuna is not far from the military airfields and SAAB fighter airplane factory of Linköping. When working at the site, we have constantly been overflown by various military aircraft. The larger cartridges are traces of a fighter pilot’s shooting practice one day decades ago.
Is there perhaps a gun nut around who can give us the type codes for the two ammo types?
(Kai, guess what I’m gonna give you as a housewarming present.)
Update 26 September: Explains Felix, the larger cartridge is likely a .50 BMG whose production began in the late 1910s. It was used in fighter planes especially during the Second World War.
Update 27 September: And N.N. adds that the smaller one is likely a 6.5×55 mm Swedish Mauser cartridge, developed in 1891 and popular among hunters to this day.