This is the flush fitting 4 round .17HMR factory magazine for all Anschutz .17HMR rifles (1517-U4 012961).
This is the third version of the magazine, re-released in November 2016 with an all stainless steel magazine body.
Anschutz currently don't make a higher capacity magazine for the .17HMR so most people carry a pocketful. Though some customers have reported it is possible to grind down the follower legs slightly to take five rounds.
If you have an older Anschutz HMR which came with a blued magazine we recommend the .22 WMR version of this magazine which run better on older types.