In the past, installing a magazine tube extension on one of the 870/1100/11-87 series of shotguns was as simple as removing the mag cap, prying up the magazine spring retainer and swapping out springs before screwing on the extension. With the advent of the detent style magazine spring & mag cap retention system this is no longer possible. Now one has to find a way to remove those detents so the follower can slide past them. The most common solution is to grind them away from the inside; while effective, this looks terrible and creates two ready access holes in the mag tube for dirt & other debris. XS® Sight Systems Magazine Tube Swage will allow you to easily remove these detents without creating these holes.
Big Book Catalog, Issue:73, Page:482