.17 Mach 2

[Cossack]

Light on recoil, somewhat faster than 22 (1750 fps) but tiny bullet is affected by wind and lacks kenetic energy (KE) much beyond 50 yrds. Made to sell ammo (rimfire), just not getting much acceptance because of ammo cost and poor KE.
No comparison to 17 HMR. And while flatter, less terminal performance than a hyper 22 at 1450 fps and a bullet twise the weight of Mach2.
But, look at the cartridge, sure has got cute going for it!