Well this is embarrassing.
The mixed headstamp thing got me thinking and I decided to retrace my steps here and started with redoing some plunk tests. While some did pass, most did not. And its not necessarily one headstamp or another that passes or not. I had originally set my dies up with new starline brass and shortly after got my hands on 2500 pieces of once fired at a very nice price and have been using it since. Dont know if that would affect die settings but i suppose the evidence says it does.
Meplat on my boolit is .270
Meplat on the sig bullet is .215 and has a slight roundedness transitioning from the cone to meplat.