G'Day Dave, I'm guessing your mate's calibre of choice is 5.56mm? (.223)
I used to yack with a guy just like him in Colorado, he was a CB750 guy and gun nut (in a good way) and made his own custom riifles, but used a modified M16 to shoot Groundhogs for a couple of local farms and had a camo electric Golf Buggy that he used to drive around the farms to pot Ground Hogs. He could drop a Hog from several hundred yards away, and was very popular with the local farmers.
He got real sick a few years ago when he got sprayed by a crop duster whilst in his camo buggy, and I haven't heard from him in the last year or two, I know he had a pace maker put in, I hope he's still around? I can't remember how I met him online, probably via eBay I guess? Nice guy though, but a real "No Nonsense" type, he wouldn't even consider getting some sort of compensation from being sprayed? Cheers, Terry.