I'm interested in getting my mining from 75 to 85, and have been reading guides. Nearly all of them say at something like 40+ with a rune pick you one hit iron nearly all the time. At 75, I maybe 1-hit iron 1/25 times. Generally it's right after the first 3 "scrapes" of the rock are done though. Is that what is meant by one-hit? Or do they literally mean instant pick goes down iron goes in? Just interested in clarification.

Before the mining animation update, you'd just swing your pick up in the air, and you'd get the ore before your pick comes down, sometimes it'd come down and then you'd get it, but that was one hit mining. Now the graphic update came into play, and it usually takes the few scrapes.