You didn't mention what primers you were using? I had that issue with plated bullets and w231 and I was using 4.0 to 4.4 gr of powder but I was using CCI primers. I was also getting squibs and they were a rreal pain in the ***. I quit using the CCI primers and the problems went away. I also have used Winchester small pistol magnum primers and saw no difference in the way the powder burned. Accuracy was the same also.