I grabbed some IMR 4227 and headed to the range for some load development. I started at book minimum 14.0 grains pushing 158 grain lead laser cast. Group was fairly small. Switched to 14.4 grains and the group got even tighter. I will show targets once i get my photos later. Went back to 14.0 and shot another 6. Gun cylinder would barely close and would barely rotate. I took it home and noticed lots of powder kernels under the extractor star. Cleaned it up and all is well. My question is what causes unburned kernels? Was the charge too light? I was using magnum primers and using my Ruger GP100 Wiley Clapp.