Here is the readers digest version. I was cutting a head leaning tanoak and it sat down on the bar when I made my gunning cut. I unscrewed the powerhead and the tree fell on its own.
Ok now here is the long version. I went into this area to fall 2 marked trees, this tanoak and a big leaf maple. I could not find the maple and I had planned to cut it first. The tanoak is fairly large and needed my full concentration. I was distracted because I couldn't find the maple and I just did not have my head in the game. The 660 has a 36" bar on it so you can see the tanoak is about 32" in the narrow (leanng) dimension and about 40" in the long dimension. I started the gunning cut without walking around the tree and inspecting it. The gunning cut was made right through the only solid wood and the tree sat down hard on the bar and started popping loudly! I ran back to the truck and grabbed a scrench and another saw, then grabbed my camera. I snapped the first 2 pics in 15 seconds and made a dash for the saw. Fortunately I was just doing my final aiming on the gunning cut so the saw was not dogged in deep! I unscrewed the powerhead and pulled it out. The tree came down on its own with 25-30 seconds. You can see the imprint of the bar on the stump in the last image. An 8" section of the bar is pinched closed and will need repair.
The funny thing is that I have been waiting for an Oregon LW bar from Bailey's. It was on back order or I would have used it here. It was waiting for me when I got home. The maple was on the road on the way in, I drove right next to it. The tanoak fell 30' of the lay but was OK, just a little harder to clean up. I took out two 18" dbh trees when it fell and left a nice tree fall gap.
Here is a pic of a newly marked take tree. My wife has a very sore back so this is not a pic of her best smile. My daughter has chicken poxand did not want her pic taken at all.