The shotgun will be sitting in the R shoulder pocket when you're pulling back. Because of the length of the vertical grip, you to tend to pull the base of the grip towards you and that twists and torques the action bars, causing them to bind or drag in the receiver slots, and even on the barrel when it's really bad.
Lubricating follower/spring/mag tube on a pump action shotgun. Yea or nay? Does one add any lube to the inside of a shotgun magazine tube or does keep one dry to prevent fouling? I have an 870 with a +2 mag extension from Wilson's combat and I hear that scrapey scrapey noise when loading up the shells.