As it has been stated extremely well; HEAT kills barrels. 3 shot strings and let barrel cool down to touch naturally or get a small battery powered bait bucket aerator to push air down the barrel after each 3 shot string to help cool it down faster. They work, are cheap and you can make all kinds of crushed ice water systems to push air through to enhance cooling air down the barrel. One of those large crazy plastic straw glasses where the straw spirals around in the glass is perfect for easy conversion. Just add crushed ice and water and hook up the pump and voila! I do most of my main shooting in winter for this reason plus hardly anyone ever at range. Good exercise to walk through snow to target berms too! The exertion will help test your breathing control!