For those converting the 4013, 4053, I remember having issues with the crimps on the sides of the magazines that secure the spacer interfering with the follower. Had to take a pillar file and remove some material off of the protrusion from the inside of the mag body in order for the follower to work smoothly.

After removing the material, you may need to wrap the file with a very fine wet/dry paper or crocus cloth to polish the places where the protrusions were removed....basically just smoothing the rough crowns on the inside surface. The inside of the magazine should look as clean as possible, and be free of any defects.

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Ret. LE, FA Instr, S&W Armorer