This is the Umarex 20 round magazine for the Hammerli Tac R1 - also fits the following Carl Walther .22 Tactical Series rifles:
Beretta ARX160 .22LR (part 574602)
Colt M4 .22LR (part 576600)
Colt M16 .22LR (part 576600)
HK 416 .22LR (part 577610)
HK G36 .22LR (part 577610)
Originally developed for the Carl Walther .22 Tactical Series the licensed line was discontinued in 2015.
The popular HK 416 model was then relaunched under Umarex/Walther owned brand Hammerli in 2018 as the Hammerli Tac R1 and Tac R1 C.
The magazines haven't changed so are compatible with all types.
Manufactured from tough polymer the magazine is strippable and features a full length bullet window and spring button.