Good ole Lahti 20mm. I transferred one for a customer about ten years ago, and they are huge, heavy beasts. They can use lightly modified US 20mm projectiles turned down on a lathe to fit the necks of the original Finnish cases. Most owners also make or have made their own new brass cases machined (rather than drawn down) from brass round stock, and cast or machine their own projectiles, too, since even US 20mm projectiles are relatively hard to come by.