Point of impact shift, I want to understand why...

Your basing everything off one group on one day....go out again without changing anything and see if you get the same results see if there is a developed pattern.
 
Just a tip - take it or leave it. Traditionally a lot of shooters zero their rifles at 100 meters with a small number of rounds (i.e. 3-5 rds) and believe that their rifle is good to go for longer range shooting and it is based on the idea the premise that their rifle is sub-MOA or close to it. The thing is that most rifles don't shoot 1" groups all day despite the internet hokum you will read - a more accurate measure of precision is to shoot longer strings (i.e. 15-20 rds) as it will show a more accurate mean point of impact and group size. The larger the sample the more accurate your understanding of your rifle will be. This will allow you to shoot longer ranges with a higher degree of precision.
 
You did not mention the make of gun, barrel taper, or whether the barrel is free floated or not.

I had a Ruger M77 in .30-06 that tended to string vertically as the barrel warmed. The barrel was very light, and had a lot of taper so as it warmed the contact pressure changed, and it strung up like your rifle. You might check to see if there is a pressure point, and check to see when you shoot if the pressure increases (use a piece of paper between the barrel and the barrel channel). In my case, the rifle went from stringing to beautiful round groups that consistently stay under 1" at 100 yards with handloads once I free floated the barrel. It is possible for some barrels to react this way with heating as well because of varying residual stresses from machining. If the issue is ammunition temperature, it can take the rifle harmonics to a bad place as the velocities change. If it is due to barrel expansion or deflection from residual stresses, different loads should string vertically when they cause heating.

If it is a harmonic issue, then changing loads / bullet weights etc can eliminate it, and certain powders are much less susceptible to changes in temperature. If you don't reload, then you may need to try some different ammo.

Unfortunately, if the stringing is due to residual stress, it may be difficult to eliminate, except to take more time between shots.
 
Glock4ever said:
Just a tip - take it or leave it. Traditionally a lot of shooters zero their rifles at 100 meters with a small number of rounds (i.e. 3-5 rds) and believe that their rifle is good to go for longer range shooting and it is based on the idea the premise that their rifle is sub-MOA or close to it. The thing is that most rifles don't shoot 1" groups all day despite the internet hokum you will read - a more accurate measure of precision is to shoot longer strings (i.e. 15-20 rds) as it will show a more accurate mean point of impact and group size. The larger the sample the more accurate your understanding of your rifle will be. This will allow you to shoot longer ranges with a higher degree of precision.
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I agree with this comment with one caveat: for purposes of hunting or varminting where you can either wait, or are unlikely to shoot more than 4 or 5 shots quickly, long strings in a light barrel can cause significant heating leading to throat erosion unless they are spaced far enough apart to avoid excess barrel heat. My .30-06 shoots consistently as long as I don't let barrel heat get too high (after five shots in less than 1 1/2 minutes my rifle barrel will burn my hand). If you wish to shoot long strings, you will probably have to slow down to avoid excess heat, especially if you have a steel (not stainless) barrel. Erosion increases with barrel temperature, and life can be reduced if the barrel bore is not chrome lined, nitrided or stainless to resist throat erosion.
 
I would add that doing hold over instead of adjusting your scope so you can focus on the target not the best Idea for a good group
 
The ambient outside temperature doesn't affect your cartridges performance. I use to shoot in competitions on different temperatures using the same cartridges and the group was in the bulls eye still...
 
Julian S said:
The ambient outside temperature doesn't affect your cartridges performance. I use to shoot in competitions on different temperatures using the same cartridges and the group was in the bulls eye still...
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You may well have but you are dead wrong. The outside temperature affects the temperature of the case, and then primer and the powder, potentially slowing down the reaction of both. Some powders are relatively insensitive to temperature change, and have the same oxidization speed across the board. Other powders are very sensitive, and can cause very erratic results when subjected to changes in temperature.
 
Did the lighting change during those shots that seemed to drift away from zero or point of aim?

Doesn't seem like you were too fast between shots however that's barrel dependent and will walk impact when heated up too fast as mentioned earlier.
 
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