I bought some alleged 378 Weatherby Magnum brass that, though it's headstamped 378 Weatherby, is actually 30-378 Weatherby brass. I have some questions:

1. What is the liklihood that I could resize the brass to 378 Weatherby without splitting the necks or collapsing the shoulders and, if I did so would I have to anneal the necks. My practice is to buy brass that doesn't need much resizing caliber wise so I've never done as radical a resizing job as .308 to .375 caliber.

2. Does 30-378 Weatherby brass generally come with a 378 Weatherby headstamp? Some of the brass looks brand new so I'm thinking it came from the factory that way.

What is the probability they were 378s to begin with and someone necked them down to 30/378? Weatherby chambers in the neck are cut pretty sloppy and many times I neck down the 378 or 338/378 to take up the chamber slop. They should be fairly easy to open up but use lots of lube and do it in steps.