HK Mark 23Superior equipment for the best units. The H&K Mark 23 defeated all competitors after being subjected to the toughest comparative trials of the US Army Special Operations Command. It was adopted under the designation MK23 MOD. O, US SOCOM. The tests which had to be successfully passed included the following: 30 000 round endurance firing test with + P ammunition Test at extreme temperatures + 73C 50C 96 hour salt spray test Sand, dust , mud test 96