A buddy of mine brought these to me the other day and was wondering what they were. They are brass cased, rimmed, center fire projectiles. The projectile is threaded at the base and approximately twice as long as the case. The only conclusion I can come up with is that they are launching projectiles designed to be inserted (screwed into) a larger projectile, possibly a mortar or rifle grenade. There is no headstamp on any of the cases but they are all painted with a different color. I assume the paint is to identify different powder charges for ranging.
From left to right: unknown, 5.56nato, 300 blackout