That will depend on the gun and the barrel thickness. Heavier barrels heat slower and take longer to cool, while thinner lighter barrels will heat more rapidly and cool sooner. The thinner barrrels will be the most affected by temperature extremes. For most purposes, if you use quality ammo, and not mutant-grade reloads, the shots should be consistent. Also, find out from your gunsmith, or the manufacturer, the best bullet weight that your gun's barrel twist will spin consistently. With my sako, 140 or 150 grains only. Anything else gives me more erratic groups, even with a sandbag rest. And what I should have pointed out first - make sure the bedding screws are tightened and the scope mounts are tight. I had a rifle loosen up on me when sighting it in. I thought the scope was way off. After my gunsmith picked it up, I noticed the entire barrel and action were rattling around in the stock with about a 1/4 inch of side -to-side play. Boy did I feel ignorant. Anyhow, hope that helps some. Curious to hear what you find out.