Smith&Wesson M&P9 mag add-on

A +4 extension for M&P9mm 17 round mags. Might have to remove a little material off of the bottom of the follower. Printed with Hatchbox PLA at 20% infill for proof of concept. One thing I did was remove the plastic covering on the lanyard loop to provide clearance for the back plate. A $4.00 part from S&W. Extra power springs are recommended. Brownells HIGH CAP S&W M&P EXTRA POWER MAG SPRING 078-000-168.