[Jack]

"At the risk of showing my ignorance, why would he use a "shotgun battery cup primer" in a rifle metallic cartridge case?"
I believe Larry was using a bit of hyperbole to illustrate how the load being discussed expanded the primer pocket and ruined the cartridge case. A rifle case that would accept a shotgun primer would be expanded enough to indicate a truly horrendous overload.
I completely agree with Mr 16 gauge about using data someone posted on the Internet. Too much possibility of typos- and bad judgement.
I have noticed that most rifles on the Internet shoot 1 inch groups or less. Those rifles seem for more common than the rifles I see in use at my local range. That's always made me wonder about the veracity of internet loading data, as well.