So have you guys ever heard of some of the crazy overbores made from the 10mm Auto? I’m sure most if not all of you know that .357 SIG is a 10mm necked down to 9mm, but they only get weirder. First picture here is .17-357 RG (for RealGuns), a .357 SIG cartridge necked down to .17. I’m not honestly sure why this was made, but it’s just hilarious, and apparently surprisingly accurate with insane velocities (over 2000fps) from a 4” barrel, though it doesn’t have the energy to cycle a semi-auto’s slide.

The second is .224 BOZ, a 10mm Auto cartridge (later using .357 SIG casings for ease of necking) necked down to .224. This was originally made for 1911-style pistols (as shown) and loaded with surplus M995 bullets, to give a handgun armor-piercing capabilities using a readily-available projectile. The cartridge was a success in penetration tests, but the massive case neck caused frequent jams and thus was abandoned in favor of the then-new 5.7x28mm round.