300prc to 375 ruger ?

[Dean2]

My experience with sizing up brass is limited to just my Contender in 357 harret . It's cut down 30-30 then necked up to 357. With this I tried to size up without annealing and would split necks . After I annealed I had no problem . This is a different animal as it's necked and has a shoulder . I'm going to test every option and see what gives the best results. I'm just happy as heck it works. I'm thankful for all the help also .

That is a different animal for sure. In this case you are cutting the 30-30 brass down about .3 and then forming a new neck and shoulder into the brass that comprises the actual body brass, which is a lot thicker, while at the same time, trying to neck that brass to 357. That one, I would anneal too, before trying to size it.