Lightened Bolt Catch Spring$3.25
Magazines like the S&W 15-22 have a strong enough spring to solidly engage the bolt catch after the last round is fired. Some magazines like the KRISS Defiance DMK22 need a bit of help to consistently engage the bolt catch.
This spring is a direct replacement for the stock bolt catch spring and will allow you to use the DMK22 magazines with the Catch22. There aren't any adverse effects from switching to the lighter spring.