You mentioned that the chamber was .004” larger then the FGMM..but didn’t say what it was compared to the PPU that was really tight. Did you mean to say magnum powders or magnum primers? If your using magnum primers in the .308 your likely going to get weird velocity fluctuations due to the spike in flame. These spikes will give you vertical stringing at longer ranges. I loaded for a custom 300wsm for years for extreme long range shooting and used “standard” large rifle primers in it which holds a lot more powder then the .308. The mag primers were necessary unless the temperature dropped to below 30 degrees.

You got really big jumps in our powder charges with the RL15…I don’t know off hand what the max is for that..but jumping from 41.9 to 43.6 is too much. All initial charges should be spread apart by .5grains..you could easily miss an accuracy node with those numbers or get into a pressure problem quickly.