[Canadian Psycho]

Its more of an issue with high magnification scopes on precision rifles in high-round count situations. Some bench resters will actually run fabric strips suspended over the barrel to minimize distortion. As far as real world situations, you're not gona notice it a whole bunch when rounds are flying at you. Its basically a non-issue. With my AR, even on high round count courses I've yet to have an issue with an distortion by heat rising from the barrel, sweat dripping on glasses yes, mud/rain on optics yes, but not heat distortion.