Local gunshop curator (it's that kind of place!) showed me something he recently got. It's a vintage 50-70 cartridge with a wood bullet. An initial google comes up with several references to such a round being produced in 45-70 and referred to as a 'forager round'; it contains some birdshot and meant for close range small game shooting (?). I'd guess the wooden sleeve acts as a shot capsule for getting down the rifled bore (?).

Anybody have more knowledge on this cartridge?

Matt, love to see an image of it. Is it inside primed? I once found three .50-70 cartridges dropped by some infantryman in a seam in the lava at Captain Jack's Stronghold, site of the 1872-3 Modoc War in far Northern California, and they were all inside primed. I even managed to leave them where they lay!