CH, I have shot OO Buck through a Remington Ventilator which I believe has the same constriction as your Undertaker. Nothing blew up and I fired at least 4 rounds through it. However, the pattern was awful. I was trying to find the tightest pattern for deer hunting and that was not the way to get it. The big pellets do not like to be squeezed down that much, they scatter worse than with a mod. or full choke.
Because #4 Buck is so much smaller than what I was shooting it might not scatter as much. I do not know. The bigger question is, could you have changed shells in the chamber without spooking that yodel-dog away?
I know this though, if I am hunting and a coyote comes within range of me I am going to cut loose at him unless I have #7 or smaller in the gun. They have decimated the small game in my hunting area. Better luck next time!