The only time that I ever used nickel plated cases was, and still is for a .280 Rem. A-Bolt Browning rifle. I have never had a problem with them. I however have not purchased anything else but brass cases since. If the cases are new and unfired, they should fit perfectly. I suggest measuring one of the cases prior to resizing and after resizing. Then carefully check all the data in one of the better reloading manuals with the data that you have. I suspect the problem is that the cases have been fired in another rifle and need to be full length resized. If not, try to adjust your dies to the proper dimensions.