Yes, reading the caption suggests that the nitro proofed .303 is the same size as the 450BPE leading one to believe that the designers felt that the stress of a .303 is similar to a .450BPE, but this in no way could be extrapolated to suggest that it could take the pounding of a medium or big bore nitro express load.

I'm with Curl on this one. If one wants to potentially destroy what by all accounts appears to be an incredibly beautiful rifle by stressing it well beyond its design parameters by using a .400NE or .450 NE load in it, that would be a serious pity.

What we do know is that a .450BPE load should work based on the manufacturers building it in the .450BPE.