My BIL showed me a neat 870 at Christmas. It had a 12" barrel, an extra ammo carrier and a light. He planned to take the light off, made it too bulky. The magazine had 00 in it, with slugs in the carrier. The stock was 2" shorter than normal,to deal with body armor. I happened to mention the pistol grip. His reply was the only way to shoot, would be from the hip. Otherwise, result would be as you described.
I shot from the hip. and BRACED into the hip.
I wouldnt shoot that kind of load without a full stock