In my experience burn rate has a lot to do with great loads. Although a you are trying similar burn rate powders there could be just enough difference preventing you from getting to the sweet spot. Take my 308 for example. I had read that Varget was the go to powder and I tried working up loads from start loads all the way to flattened primers and sticky bolt lift and it just wouldn't come together for me. Switched to the old faithful IMR 4064 and the rifle loves it half inch or better groups. Very small burn rate difference between the two but vastly different results on paper.
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