This is the Promag smoke 22 round .22LR magazine for the Remington 597 semi-auto rifle.
Made from a see through smoke tinted plastic, with nylon follower and chrome-silicon spring, it is fully functioning with the 597 last round bolt hold open feature.
You can’t go wrong with having extra magazines, whether it’s for quick loading times at the range or in the field. Or, as a backup in case you lose one or drop one in the mud.