Pardon my ignorance, but why would it be necessary to bush the firing pin hole just because the cases were made for small rifle primers? Various switch-barrel guns have been working with one firing pin for years.
I also have to take issue with the notion that a manufacturer would be liable for some goober's assumption that the small primer is a license to go batschit-crazy with pressures. That's similar to saying that Cadillac, by making a 600hp motor is suggesting that its okay for someone to drive at 200mph.
Lastly, I don't know a great deal about "gas guns", but from my reading it seems they are pretty good about letting you know when you're getting too frisky with your loads.
