Wait a month or so as the ammo shelves fill back up, and buy a box of as many kinds as you are comfortable with.
From my experience, one of the rifles will "prefer" a different ammo than the other.
And, also from my experience "you" are a significant part of the equation, too.
You find an ammo that is tight for you and the rifle, pass it over to another, and the group will change.
Also, given that most folks only expect their "dirty-dirty" to hit minute of pie plate (while being capable of better) so "target ammo" and .30-30 will have less of an "equals sign" for many folks.