An in-reactor polymer blend including a propylene-containing first polymer; and propylene-containing second polymer having a different crystallinity from the first polymer. In an aspect, a magazine block device is provided having a bullet-shaped body, two upper ridges forming a longitudinal channel through which the firearm breach face loading tab may pass without dislodging the magazine block device, and an offset lower ridge. Each jacking member includes a respective jackscrew that is rotatable for applying a wall holding or a wall restoring force to either or both of the upper and lower sections of the wall.