Noz,
I am not sure where your square load of powder comes up to, but I had some issues very similar. I always used the red Winchester wad over 65grs of Goex in my 12ga loads. I had to buy some substitute red wads after Win quit making them. When I started in using them, I had hulls that bent, kinked and would not crimp on my Mec loader. The problem was that the early red wads were too hard, the legs would not bend when compressed and that caused the whole problem for me.
I contacted the company that makes the wads for Claybuster and they told me they changed the plastic formula and sent me some samples. The new ones work every bot as good as the ones that were made by Winchester. All I ever get is once fired AA hulls any more and they all have that two piece design. So, if you are catching the edge of the second inner piece of plastic at the bottom of the column and are using a red Claybuster wad, it could be an old batch and they can tell that by the small label strip with a a number on it that is applied to the bag.