Tom , I experienced this situation with 6.8spc rounds loaded into 223 mags with a 6.8spc floor plate. I could only load 18 to 22 in a 30rg mag. The thicker bullets would not roll freely up the mag with a fully loaded mag, you will find out what your limit is. Also check the feed lips of the mag for interference , a trim on one mag may be in your near future as a test.