I'm gonna go out on a limb here and say the reason some companies won't chamber an encore for the weatherby mags is because they are loaded to 55,000cups instead of the regular 54,000cups that the standard(300win mag,338 win mag, 264 win mag,etc, etc...) magnums are loaded at. Plus like what was mentioned before about the freebore, its my understanding that this also helps in keeping down pressures, so if you put a top weatherby load in a non-freebore gun it could cause pressures over 55,000cups which I imagine is a lot of pressure for a encore(or any break-open single shot) to take over a period of time. An encore, I suspect, will not take the abuse a good strong bolt-action will. Dave