Your buckled case shoulder was likely due to the seater die body being set too low and the crimp shoulder pushing down too hard on the case neck. The Lee help video for this is here
. If you don't want to use a crimp (I don't usually), just don't follow the last instruction to turn the die in a half turn, instead turning it out a half turn, then checking the seating depth adjustment once more.
To gauge case shoulder setback for sizing die setup, you just need to know where the shoulder is on a fired case and that you set it back below that level. -0.001" below fired case for bolt guns, and -0.002–0.003" for gas guns. You can check this with a caliper and a spacer whose through-hole is about the size of the middle of the shoulder. Below I've used a hardware store bearing journal bushing instead of a spacer, because it was convenient, but spacers work, too. In the photo the .30-06 case is 0.003" bigger than a headspace gauge I had zeroed it on previously, but just zero on a fired case and see that you get the -0.00# number you want.