G2 frames are supposed to be able to withstand much more pressure than you listed below. Without getting into a bunch of numbers, it is safe to say that buckslayer can load his G2 Contender with any factory ammo and not worry about it. It's only if he starts handloading will he potentially come across any pressure issues.
I wonder where you heard that G2 frames are supposed to handle more pressure than I listed above. I've loaded the .45-70 for over 35 years and am well aware what T/C recommends - having personally asked them. That would be
Trapdoor-only loads, which encompass
NORMAL pressured factory loads from Remington, Federal, and W-W. Not "non-Ruger No.1" loads, not "Marlin-level" loads, but Trapdoor-level loads.
Apparently you are unaware of what loaded ammunition is available on the open market. You and I can buy "factory-loaded" ammo which substantially exceeds Trapdoor levels of pressure (Garrett, BuffaloBore, etc.) and which would
not be safe in a Contender. You don't have to start handloading to get into trouble.
Since the OP asked if the G2 could handle loads as powerful as an Encore can - the correct answer is a simple and unqualified NO.
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