Magazine Extenstion for Anschutz 1420-U13 Magazines. Requires use of follower and spring from CZ 455 10 round poly mag (#12004) or Savage mk2 10 round mag ( #20005) - either follower will require bending (CZ) or trimming (Savage) to tune the fit for proper function.
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I bought a couple of these. Wound up having to buy two Savage mags to rob the springs and followers. Then there is some minor fitting to the follower.
Do they work? So-so at best with a full 12 rounds. If you have never owned an Anschutz then be advised that the magazines are not perfect. Mine run great 99.5% of the time but you must take care not to get "rim-lock" when loading them. In fact, in the downloadable manual it has a section devoted to loading them.
I wish, even with what seems to be some issues, L3i would come up with a plus rounds mag for the Annie.