HELP!! 270 WSM not working

[300 RUM]

My neighboor came over with a die to reload some 270 WSM. He had a mix of nickel and brass cases. He thought they were all trimmed the same. After loading a few we found all the nickel cases will load great into his gun but none of the brass will. I coated the bullet with dry erase marker then tried to chamber them and it looks like they are hitting on the shoulder where it starts to taper to the neck. By measuring with a caliper they appear very very close but they will not chamber.


Any suggestions Please