US Patent 7752977 Deceleration apparatus for projectile

A decelerating apparatus includes a sleeve having a forward end and a rear end. A plurality of helical grooves formed in the sleeve. Each helical groove begins at the forward end of the sleeve and has a depth that decreases from the forward end of the sleeve towards the rear end. The depth of each helical groove at the forward end of the sleeve is large enough so that the helical groove cuts completely through the sleeve at the forward end. The plurality of helical grooves define deformable petals therebetween.