Another thing to check is case weight. I've noticed two significantly different case weight groups with the factory loaded Hornady brass. The first group weighs around 219 grains and the second group weighs around 224 grains. The five grain difference will affect pressure, especially if you're already pushing on it a little. What primers are you using? Standard or Magnum?It's weird it will only do it on maybe 3/5 rounds. My theory is the RL26 is temp sensitive and if you take too long to shoot it will "cook" in the chamber. The ejector marks are smears. Very very heavy bolt lift/ Velocity is low around 2900-2950 with a 147. primers look fine and pockets are still tight but only 1 firing on the brass.