I've been cutting rounds from a large frozen dead oak I felled the other day, about 30" wide. Just had the chain sharpened by my local Stihl shop, (no I don't sharpen myself, I don't know what I'm doing!) After 6-7 cuts, not all the way through as to stay away from the ground, I'm getting the half moon drifting cuts at the bottom. Every cut gets progressively worse. Can that big thick frozen oak be dulling the chain that fast? This is what the dude at the Stihl shop says but I've never met him before if you know what I mean.