POI moved

[hundmeister]

Hi. I'm wondering what causes this usually doesn't concern me but am curious what makes a rifle do this. Was testing reloads twice last week and noticed that my groups shifted point of impact. I'm very happy with groups just curious what causes this and if you run into this as well. Tikka varmint 22-250 optilocs viper 6.5-20 groups are at 200 yards.
One of you guys suggested trying 33.8 34 34.2 ish at longer range and looks like it came together at 34.2g varget 52g varm. berger. The conditions were very much the same maybe a slight breeze to the left on top target and more humidity on bottom. bottom had zero wind.

 

[ColColt]

If it were me I'd check the bedding first. It could be the stock as the barrel heats up, is pressing against the barrel at some point. Secondly, I'd check my consistency at the bench. A tighter grip that previously, check for the front/rear bags being on axis(although being off is more for horizontal stringing) and watch for variations in where you have the fore end. I once had a similar situation and watched as I repositioned the rifle after recoil and the sling stud was resting on the front bag...you don't want that.

 

[Ridgerunner665]

Parallax maybe...

 

[hundmeister]

Viper adjusts parallax

 

[Darkhorse]

I see this quite often when load testing. Some bullets are more susceptible than others, regular Ballistic Tips move a good bit but the Ballistic Silvertips pretty much retain POI. This is in my 7mm mag.
I'm convinced, and my load development is based on this, that it is barrel oscillation that causes the POI to move. Small changes in seating depth, and to a lesser degree powder charge, causes the bullet to exit the bore at a different spot in the barrel oscillation.
If you were shooting at 100 yds. the distance your POI is moving would be negligible and maybe not noticed. But at 200 yards the change is doubled and becomes more noticable.
I try for the best shooting load, tightest group at most velocity if a hunting load. Then sight in that load knowing that if I change anything I must check the POI again.

 

[Ridgerunner665]

Viper adjusts parallax

Ok...could you explain your procedure for adjusting parallax?

Not trying to ask dumb questions....but many people don't do it right...the numbers on the scopes are never correct, and often when adjusted for zero parallax....the scope will be slightly out of focus.

 

[hundmeister]

Left side knob on viper should adjust focus and paralex Viper PA for paralex adjust.

 

[Ridgerunner665]

Yes...but if you're going by the numbers on the scope, there's a 95 percent chance it's not properly adjusted.

Aim at the target, move your head side to side....if the crosshair moves on the target...you're not properly adjusted.

Those numbers are not correct, were never meant to be....same for focus, though it should be focused when parallax is set...it's usually not....I had a Viper HS, it was always a little out of focus when parallax was set properly.

Forget the numbers are there...move your head to find the proper setting...won't cost you anything to try it, and may well be what's wrong...you may have to turn it all the way to the "infinity" mark....but when the crosshair stays still when you move your head, you have zero parallax.

This is just one of those things that it is very expensive to avoid....very high dollar scopes are required.

This doesn't mean your scope is broke...this is common on all of them...many makers don't put numbers on the parallax knob for this very reason (Zeiss for example)

 

[Ridgerunner665]

You can also avoid this with a very consistent cheek weld...but some stocks are better for this than others.

 

[NYDAN]

I have seen my POI move after cleaning barrels. I speculate that sometimes differing residues or amounts of residue in the barrel lead to differing POI's.

 

[ColColt]

You can also avoid this with a very consistent cheek weld...but some stocks are better for this than others.

I had a Weatherby Vanguard in 270 that I had to give up on. I held it like any other rifle I have and it smacked me good in the cheek with any load. I traded it.

 

[rquack]

Was there any significant change of temperature between the shooting sessions????

 

[Oldtrader3]

I usually move group centers like that when I have changed my hold on the rifle, my shoulder seating or my cheekweld position.

 

[Ridge_Runner]

how about the angle of the sun on the target, your perception of where the crosshairs are at changes as the light changes on the target, my POI will change a bit from full sun to overcast,
RR