There are certainly semi-auto paintball guns, so I don't know why they didn't use one. The Heinyman would have probably equaled Adam's kill count before going down.
It was hysterical that Jamie showed up with half a dozen guns and bandoleirs of spare mags ("optimistic of him," I said the the mrs.) and didn't even finish one clipful.
Yeah, I figured there'd have to be some semi-auto paintball guns out there, give him a single-action gun he had to recock and then aim after every shot seemed like a huge handicap. I guess you *could* liken that to a shotgun or many rifles but, still, it would have been nice to see them simulate a semi-auto weapon.