My two favourites are poles apart:
.22LR and .44Mag!!
And for rifles there is 22LR to .348
And for shotguns there is .410 to 10 gauge
Love them all but 22 still gets shot the most.
Good intentions will always be pleaded for any assumption of power. The Constitution was made to guard the people against the dangers of good intentions. There are men in all ages who mean to govern will, but they mean to govern. They promise to be good masters, but they mean to be masters.