I own two 300ultramags and have owned a 300wby and loaded for a second one.The ultramags produce about 100fps more with 180gr handloads.The ultramag factory loads are very mild so I would not bother with any ultramag if I didn't reload.On the other hand the weatherby factory loads are very hot and I was only able to reload the fired cases once or twice afterward before the primer pockets were too loose to properly hold a primer.