The 6×51 Atzl is one of two wildcats which were designed by Andreas Atzl and CIP approved in 1997. The 6×47 Atzl was based on 222 Remington cases produced by Hirtenberger and necked up to 6mm. The 6×51 (aka 6×50) Atzl  was based on lengthened 222 Remington cases and was commercially produced by both Hirtenberger and Horneber in 2003/2004. Originally produced without hs (by HP) and later with a proprietary “ATZL 6×51” hs by Horneber. Below is the SHM version.