I believe it's a Federal law that gunmakers must test fire all guns before shipment and put proof marks on them. I know Ruger and I'm sure most other Mfgs use a special test ammo that is loaded to higher pressures then what's available to the general public.
My thinking it's possible the higher pressure cause more copper fouling.
Last edited by Ruger-Redhawk; 04-06-2010 at 09:47 AM.