Ken, that barrel bending can be a serious problem to accuracy in double rifles. Keep firing just the one barrel and if will soon start sending its shots wide. It the same principal at the bi-metallic strip in a thermostat. I guess shotgun shooting accuracy would suffer too but not be quite as noticeable.
Drew, I've certainly found that shooting black powder cartridges will heat a barrel up much faster than when using nitro cartridges. Try firing half a dozen BP rounds on a warm sunny day then try to touch the barrels. When I mean 'warm and sunny' I am referring to England where that would be in the low to mid 70's. Goodness knows what it would be like at around 100 degrees! Lagopus.....
