Originally Posted by Tenderribbs
That makes sense so your saying the heat does affect the bullet the third shot?
I'm saying it can, and it's possible that it can affect it quite significantly. One shot will warm the barrel. If the second shot is fired before it cools, then a third is fired in the same interval, then the third shot could be leaving from a bore that is twice as warm as the second shot, and 4 times as warm as the first.
Just an example, to try and put it into numbers. These aren't accurate numbers, and I've conducted no study to get exact figures or percentages, but with many hours behind machine guns, semis, and bolt actions, I'll stand behind thus theory of mine until or unless someone proves me wrong beyond any shadow of a doubt...
Let's say your first shot is fired from a bore at an ambient temp of 70 degrees. That shot hits exactly where you meant it to, but it raises the temp of the bore by 5 degrees.
Now your second shot is fired from a 75 degree barrel. It is only slightly off from the first POI, but if you fire it before the heat from the first shot dissipates, you may have just raised the temp of your barrel to 85 degrees. Twice the increase from the first shot, because the effects of friction (which is what's causing the heat) accumulate over continued application.
Let's relate that to inches, for the sake of simplicity. Again, I'm making up theoretical numbers for illustrative purposes.
If your second shot is fired from a note that's five degrees warmer than the first shot, it may be off a half inch. If the third is fired from a bore 10 degrees warmer than the second, this translates into FIFTEEN degrees warmer than the first, and it may be off your mark by upwards of an inch and a half! And in a different direction!
This is why thicker profile barrels are more popular for marksmanship competitions. The greater surface area dissipates heat faster and the profile adds rigidity.