resizing 7Ultra Mag to 300 Ultra Mag

[Wachsmann]

Does the 7Ultra mag and the 300 Ultra mage share the same case size and shape. I was told you only have to resize the case mouth and it will be the exact same. Is this correct or does the cases have different dimensions such as taper on the case body or a different taper on the case shoulder. If its the same I would think it may need to be trimmed after resize and since its been sized up the neck may be thinner now. Just some thoughts since 300 brass is getting hard to come by.

 

[comfisherman]

I go 300rum to 7rum all the time, since I purchased my first 7rum brass for it has been almost impossible to find.

When going 300 to 7, I full length size and then trim to length, haven't really had to neck turn anything. Its not a huge switch so I cannot imagine the brass would be terrible thin.

 

[Gunpoor]

Comfisherman is absolutely correct, both cases have a 30 degree shoulder angle and are the same lengths, the only dimension that is different is the neck size. You should have no trouble opening the necks unless your brass has been fired too many times so that it is brittle and if so you may need to anneal the necks.