I need load recommendations for COW forming 338-378WBY.

A buddy has a P17 Enfield chambered in 338-378WBY and I necked up some new 30-378WBY cases to use in it but mine are .025" shorter at the shoulder than his fired cases.

He's fired factory WBY ammo in his rifle so I could load as is but I'd like to maximize case life and not start the cases off with a stretch.

Thanks


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