This is the top line from RWS. It has a velocity slightly above the speed of sound and is noisier that normal
From the RWS Web Site
* RWS TOP cartridges with excellent shooting performance. * Preferred by internationally successful sport shooters. * Produced under special conditions. * High velocity in supersonic range. * Particularly suitable for shooting at both 50 m and 100 m. * High precision for silhouette shooting with rifles and pistols. * Also highly suitable for biathletes. * Calibre: .22 long rifle. * Lead bullet, 2.6 g, V0 345 m/s (barrel length: 65 cm)