Sun/Heat and POI change

A

AWS

Retired PM Staff
Sighted five rifles in on Thursday for a shoot yesterday(sat). I live on the coast so sight in conditions were mid 50s hazy, overcast heavier sea air. The shoot was 70 miles inland 500' elevation rise and temps were near 100 and bright sun.

My first rifle, my winter gun painted all white including the scope was right on the money. All the other rifle were 2" to the left.

Would the sun on the dark rifles or the heat cause the same 2" change in POI? I've never noticed this when resighting rifles on a hunt inland in the winter.

AWS
 
I shot yesterday in the sun/heat and had drift to the left after the barrel was hot. One thing I noticed was that after a while my heart beat was moving the POI to the left rather than up and down. Shift was inconsistent but was about 4" at 240 yards when it happened. By inconsistent I mean I had half the shots group on target and half to the left. Up and down was much more consistent.

Set up:

16" RRA 223
front was resting on Caldwell sand bag
stock was propped up on left hand
earphones on and right side was in contact with foam of ACE stock

At first I just assumed it was the heart beat and me shooting when the heart beat happened and then when it didn't (if that makes any sense at all).

Then at the end of the session I shot at the 100 yard targets and sure enough I was shooting left 2", so I don't know.
 
Was your ammo left out in the sun light for very long?
I have seen hot cases shift POI as much as 4-6"...
 
I live in the mountains of Arizona and the temp. is usually in the low 80s in the summer. If I go down to the Ben Avery range in Phoenix the majority of my guns shoot to a different poi as the summer temps can be in the 115-120 range. The heat in phoenix will cause increased pressure, in max. loads, I have to watch for loose primes. I think the hodgdon extreme powders might help. The extreme powders were designed to help with the pressure changes when changing temp. or elevation. I also keep my ammo in a cooler and out of the sun as much as possible when shooting in high tempatures and this seems to help.
I don't think a change of 500 feet in elevation would make a great difference in your poi. From my home to Phoenix there is about a 6000 foot elevation change and that will make a big difference in impact.
Hope this helps,
Tim
 
I know you said five different rifles. But just out of curiosity, are you also talking five different scopes or are you using the same scope on all five rifles with a quick mount?
 
Each rifle had it's own scope.

1st Savage 11 22-204 Sightron 1.5x6 scope stock and barrel white dead on.

2nd Rem 600 6x45mm Weaver 2x10 matte black scope 1" high 2" left

3rd Rem 722 22-250 LVSF Barrel 700ADL stock Elite 4200 2.5x10 1" high 2" left

4th Rem 700 ADL 243 Win Mueller 4.5x14 2" left(different shooter) He was able to see the fist two bullets go left and held right and took third place.

5th Stevens 200 6mm-204 Viper 6.5x20 1" high 2" left

Wild was not a factory either sighting in or at the match.

Now I have to get back to my home range and see if they are still shooting left or if they are back in the black. All of these are sub MOA rifles and have had no history of changing impact.

AWS
 
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