An easier way to kill him than having a 1/8 chance of hitting him is this:
you have to get killed by Mantis(after Campbell tells you to switch the controller port) and then continue. The next time through if you call Campbell, he will ask you if there is some reason you can't switch controller ports...then he thinks for a bit Call him back and he will say to shoot the statues with the gas masks on (that mantis throws at you), this will have the same affect as switching controller ports.
It isn't always the next time through, however. Sometimes you have to die and continue multiple times before Campbell will suggest shooting the statues. I think some people have reported having to die and continue up to four or five times.
"Ya can't do much damage with that one, can ye? Perhaps it should've been the 'rule of wrist'."