Point of Impact ?
 

How much difference in POI do you experience from a cold & clean barrel VS a warm & dirty barrel ?

depends on the rifle, I have a couple with almost no difference, and a couple that show consistant 1/4 moa varience, some go 1moa. I never hunt without fouling the barrel, If you leave oil in the barrel the difference is more, even my precision rifles give you a first round cold bore flyer of up to 3/4 moa with an oily barrel.
RR

Pretty much sums it up.

No difference in the 2 rifles I own

RR pretty much covered it....every rifle is different. My Savage Model 10 FLCP-K in 308 shows the most dramatic changes between clean and dirty. It takes 7-10 fouling shots for it to settle down and shoot well...after that, a cold barrel with toss the first shot about 2" high @100 and will shoot 1/2 MOA @ 100 all day long.

You might be a redneck if your answer to this question is..........

Not enough difference to miss the lungs on a deer.

Yes, I am one

I also have an old savage 99 in 7mm/08, shoots a consistant 1.375 moa with its favorite load, plenty good for woods whitetail hunting, clean the barrel (which I think is pitted badly) and it will not hit a 40" circle at 100 the first 2 shots, then its walking back to zero, around the 6th shot its 1" high at 100.
RR

What Ridge said. Some of mine put the 1st shot 1 1/2" high 1" left at 100. Then, they are where they are suppose to be after that. Add shooter error and it's not good lf you are taking shots at 300 to 600 yards. Your bullet is going where???????