I don't know about the O/U's but on the SXS's, the ambient temp didn't matter. I just went by the old rule of thumb of shooting when the barrels are cool enough to the touch no matter how many rounds are fired whether slow or rapid. I did notice that if I didn't have my support hand holding the gun under the fore-arm that my groups would wander. My solids and softs would often shoot to different points unless I had my hand there holding the fore-arm.