It doesn't screw into the barrel far enough to interfere with the porting.
Why doesn't he have one in the bottom barrel? I dunno, but it could be because he's a complete dummaz about firearms.
Lets face it we would all like to get him on a 5 stand with a full wallet. :-)
“Why doesn’t he have one in the bottom barrel?”
Perhaps because he was only scheduled to fire one blank
for this photo-op. A 2-3/4” shell loaded with bisquick and
enough gunpowder to push some smoke out the barrel.
Hence, the lousy stance and butt placement.
My guess is the SS didn’t trust him with more than one round at a time (if it’s really him).