There are a lot of weird and wonderful kinds of ammunition out there, but a candidate for the title of “weirdest ammunition” might be the .58 Schubarth. Shaped like an egg on a diet, the .58 Schubarth was originally designed for an American break-action breechloading rifle design from the early 1860s. The round was recently mentioned – and pictures of it posted – at the International Ammunition Association forums:
The .58 Schubarth was a variation on the pinfire firing mechanism, whereby an internal pin was disrupted to strike priming compound and detonate the round. The .58 Schubarth mated with a unique two-piece chamber, with the round protruding from one half and the other half closing on it. One major downside of the round was that it had to be properly oriented during loading, however even with this somewhat quaint characteristic it still would have been a great advance versus existing muzzleloading cartridges.