I can't begin to guess actual temperatures, but I have run shells through a 687 SPII at the rate of one shell every 6.7 seconds for three hours straight. The barrels get very hot, and you're better off using a glove on the forward hand, but no barrel problems.

This rate of shooting is not a place for a splinter f/end. It is imperative that you keep your bare fingers off the barrels themselves.

SRH

May God bless America and those who defend her.