I few years ago I picked up some temperature strips from a gunshop. They had adhesive on the back and you just stuck them to the barrel. As the barrel heated up the temp switch change colors giving you a barrel temp indication. The gun shop that I bought these from has gone out of business. Any idea where I can find more of these?

Hope this is what you're looking for.
Interesting idea. Reads like they attach permanently to the barrel???
http://www.neconos.com/shop/search/bar-l
http://www.mcmaster.com/#catalog/121/629/=vmd2qc

Thats them in the first link. They do attach permantly. They have an adheasive backing but you can get them off if you want. They work great for high volume shooting like on a pdog shoot.