Did you ever think that by the time you shot 2/3s of them that you fired all the bad ones
My standard load for the 158SWC is 3.8 grains of W231. My Dillon is always off a 1/10 or so either way when reloading.You might want to check you reloader or the way you are reloading.But it does happen I had one the other day first one in a long time.