Interesting result using resized AK brass for testing.

[StoneHendge]

I shot thousands of rounds of Starline x39 brass converted to 243 LBC (basically 6mm Grendel) back when primers were nonexistent and I had a backstock of LRPs. In addition to what everyone says above, my main takeaway was that the LRP gives faster powder ignition and hence an earlier pressure peak which is less than optimal for the cartridge and results in lower velocities for the LRP brass vs. SRP brass at any given peak pressure.