Systema M4 Slide Stock Butt Plate Button Type for Systema P.T.W. Features two oversized, spring-loaded retention locks, CNC-machined out of solid aluminum, lock the butt plate in place with absolute authority and zero guess-works. However, one easy squeeze on the side-buttons will instantly release the butt plate from the stock. Many of Systema's professional trainers were heavily involved in this design revision, and so far their feedback has been excellent. Therefore, after much deliberation Systema have decided to formally release them for competition use as well.