Range Report Large differences in windage from load to load?

[pshell]

I have a couple different loads that I shoot out of my 700 PSS. I just confirmed my base zero for my main load (168 SMK over 43.5 grs of Varget, win brass, fed primer) and switched over to a varmit load I just started to work out. I'm using 110gr SVK's, 40 grs varget and the rest is the same. I may be off on the weight, don't have my data in front of me.

Anyway, the windage zero for the 110 grain load is 3 moa to the right. I was a little shocked by this, but it's repeatable. Meaning, I could shoot my normal 168 gr load, then dial in 3 moa left and 1/4 moa up and be right on target. I did it three times back and forth to be sure. Is this normal?

 

[ChadTRG42]

Re: Large differences in windage from load to load?

Sure. You often get a different POI when switching bullets in the same gun. Now you know where each one shoots, you can re-zero without shooting them.

 

[pshell]

Re: Large differences in windage from load to load?

I was expecting a change in elevation, but not the large windage shift. I have seen the change in windage before, just not that dramatic.
Have any idea why this occurs?

 

[MitchAlsup]

Re: Large differences in windage from load to load?

The barrle moves every which way under teh stresses of the firing cycle. If the barrel can move left to right (and vice versa) what makes you think it can't move top to bottom (and vice versa), diagonally, or basically any figure of movement it wants?

 

[pshell]

Re: Large differences in windage from load to load?

Maybe you didn't understand what I'm trying to say. I get that there will be some deviation. 3 MOA right seems like a lot and I was wondering:

1. Is it normal?

2. What is it caused by, it being the excessive amount of windage.

The reason for question number 2. I shoot multiple loads through the rifle, (168, 175, 178, 180) but nothing does this but 110 gr bullets so there must be a reason.

 

[ChadTRG42]

Re: Large differences in windage from load to load?

Take a look at the link below. This shows you some different ways the barrel will flex when you fire the round. Of course it's exagerated, but you get the idea. When you shoot the 168 to 180 grain bullets, they are all real close in weight and move down the barrel with similar harmonics. When you shoot the light bullet (110 grains), it totally changes up the harmonics. The 110 bullet will stay in the barrel for a shorter amount of time compared to the 168-180's. The powders used for the heavier bullets are different than the powders for the 110 bullets. So, you are really changing up all the variables from the heavy and light loads. My 270 Win does the same thing when going from the 100 grain load to the 140 grain load.
Mitch has it right, and explained it well. So, to answer you questions:

#1- yes, it is normal for a POI shift, and 3" is not a lot of shift when changing up the load like this.
#2- See above


http://www.varmintal.com/amode.htm