Doesn't seem like an improvement over my WSM or RUM (basesd off of the 404 Jeffery) idea as once fired cases can be found by the bucket load at most rifle ranges. .500 or .512 can both be used although the .512 will have less case taper. I have even necked down shortened WSM and RUM cases down to .458. Bottom line 500 Jeffery cases are more expensive and are not as readily available with no improvement in strength. My 458GXT has case capacity between the 45-70 and 458 WIN MAG is a necked down RUM case with a OAL of 2.800 (308 Win length) which is on the same concept as the 500GXT. I think WSM/RUM style cases would be a better choice and worth investigating on your end.