I don't coddle my barrels. If I have a lot of shooting to do, I do it. To me, barrels are like the tires on my truck or my Jeep, yeah, they are expensive and I don't like having to buy new ones, but I don't buy them to sit there either and I take it for granted that if I use them for what I bought them for, they'll get worn out. Big whup...
That said... Every barrel and chambering combo is different. I figure it's too hot when I start missing. Or, if punching paper, groups start to open up. Some barrels, some chamberings, some configurations, that might not be a very long string. But some of my really heavy dedicated colony varmint rigs, I have shot strings until I could literally SMELL the steel of the barrel it gets so hot, and am still launching varmints every shot. The first .20BR I put together about 10 years ago, used to start smelling like stale sweat it would get so hot on a p-dog town. You could feel the heat radiating off it and wouldn't even THINK of trying to touch it. I'm sure that wasn't good for it. But, like I said, I didn't build it to look at it, I built it to kill things with.
Long winded way of saying, for myself, I know it's too hot (and/or DIRTY) when I start missing.
- DAA