According to Sierra both the TMKs will work through the mag when loaded normally.
I think the 69gr will be better for me as I shoot 16 inch barrels and the 77gr starts pretty slow (2700 for full power 5.56) from a 16. The extra 125fps for the 69gr flattens the shorter range trajectory and aids in getting expansion.
Both have the potential to substantially increase performance over the non tipped SMKs.
