1. Remove factory basepad by depressing the spring retainer tab located
at the bottom of the basepad. While depressing the spring retainer,
slide off the factory basepad. CAUTION! This magazine spring is under tension and can "spring out" of the magazine tube along with other magazine parts.
2.
Remove the factory spring. Remove the load assist button on the side of
the factory follower. At this point you will be able to remove the
factory follower.
3. Insert the HiViz follower and the included magazine spring.
4.
Compress the magazine spring and spring retainer into the magazine tube
and slide on the Basepad. Take note of the orientation of the spring
retainer so that the side with the single button lines up with the hole
in the basepad. The spring retainer will settle
itself into the hole in the Basepad and lock it into place.
False advertising 
Ppk/s 13+1 magazine upgrade