Ok. Well. It appears that I didn't have enough crimp. I must have mixed in rounds from three different batches, cause some from the other day fired fine, some weren't crimped enough, and some (very few) were crimped too much.
Got it dialed in now.
"It is not the critic who counts, nor the man who points out how the strong man stumbles or where the doer of deeds could have done better. The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood, who knows great enthusiasm, great devotion, and the triumph of achievement, and who, at worst, if he fails at least fails whilst daring greatly, so that his place shall never be with those odd and timid souls who know neither victory nor defeat. You've never lived until you've almost died. For those who have had to fight for it life has truly a flavour the protected shall never know."