Now, be honest. How long till dull?

Paulywalnut said:

Cutting mulberry and osage or (hedge) can eat your chain up quicker. Sometimes at dusk you see sparks fly cutting that
Osage.

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Black Locust will do the same thing. I've cut locust at dusk and it can sometimes look like a 4th of July sparkler.

You should definitely not be getting dull after 8 rounds. If you are not hitting stones, dirt, etc as folks have already covered, the problem must be with the sharpening technique and/or the temper of the steel tooth. You mentioned that you use a grinder, so if your angles are all correct, than you may be overgrinding and ruining the temper of the metal. After many years of using different methods to sharpen, I have come back full circle to hand filing. I can put an incredible edge on a tooth by hand filing, never worry about overheating, and remove far less metal than grinding. I touch up my chains with a few (3-4) light strokes after each tank, never letting them get really dull in the first place. Takes very little time to do, and works very well for me!

I can usually cut one truckload like this on one or two filings.

When the chain is cutting on a 45 degree angle its dull.

Giles said:

The greatest problem with the chains we buy today, is that they are not made from hardened steel. If they were, we could not sharpen them with a file.

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This is wrong. Tool steels are routinely tempered to varying hardnesses depending on the application, and harder steels can absolutely cut softer ones, even though both have been "hardened."

I pass the hand file 3 times on each tooth after every tank. Takes less than 5 minutes. I have two new chains that I have had for over two years and haven't touched them yet. I think angle is getting off because the current chain is working less efficiently...but at this point I have sharpened it ~20-30 times can't really say for sure. Wondering if I am just getting to the end of its usefullness. It's been through about 15-20 chords of wood. It has eaten some dirt its share of a few times, and a chain link fence once (woops).

Anyway i am getting close to changing it out.

Generic home depot chains.