I trialed a couple of pre production 261's back in 2010 I think. They were an impressive little saw at the time, I liked the new air filter system that was a rip off of the after market hi-flow system from the states. The work I do can be hard on chains so .325" isnt optimal but about right for a wee saw like the 261.
I think it would struggle with an 18" bar but it depends wether you are in a hurry or not.
We ran 391's for years, they were the saw we had on the woodchipper to deal with branches to big to feed. If you are looking at a saw in that size I would go for a MS400 instead. If the 391 is a carbed model you can hot it up pretty easily.
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