The only bullets I've ever had tumble were from too slow rifleing twist. I know aguilla makes a 60 gr sss round that will tumble from most any standard .22 rifle or handgun. I know you said it was different brands of ammo so you ruled that out. I suggest your friend send it back to Ruger with an explanition of the problem, and unless he screwed it up from negligence they will likely fix it free.