Ray: All factories that produce rifles must first test them with "proof loads" that are loaded far over the normal working pressures for any SAMMI cartridge. As such, every rifle has been fired and stamped with the proof marks you see, proving they withstood this "proof" testing.
I worked for a rifle maker here for a while, and we tested action strength by blowing up a few nice actions using a .280 Rem case full of Bullseye. When you know where they break, you can then engineer the appropriate changes in regard to structural integrity. My wife regulary purchases proof loads for a well known rifle manufacturer, and they're not sold to anyone except industry makers that are SAMMI registered.
I doubt if you'll ever find out which action is the strongest....there's just no way to prove it one way or another without total destruction.
Note: Have you seen the current email set of photos circulating of the guy who blew up the Savage 110.....owww....his hand is hamburger! (Handloading error, no fault of the rifle)
