2 Different points of impact

[bayjoe]

I have a question on point of impact.
I was shooting my 7-08 today and when I shot Sierra 168 grain BTHP they grouped 1 inch low and 1/2 right of point of aim
I changed to a Speer 115 grain HP and the point of impact was 1 inch low and 1 and 1.2 inches left of point of aim
I know two different bullets will have vertical difference but why is there a difference in right to left
The 168's were just touching the lands and the 115's are about 30 thousandths off the lands.

 

[Broz]

Most likely different barrel harmonics

 

[Gunpoor]

When a rifle is fired the barrel goes through some contortions that the experts call barrel harmonics, and the different bullets will leave the bore at a minutely different time and therefore they will impact at different points. The lighter the barrel the more drastic the harmonics but they all do a tiny little figure 8 when fired. This is why I don't use different bullets for one rifle, as I want to know where it is going to hit when fired.

 

[243winxb]

Free float the barrel. If it is already, increase the clearance.

 

[bayjoe]

I checked my stock and had a contact point at the tip on the left side.

 

[243winxb]

1/16th inch clearance from barrel to stock is good. The old dollar bill is not enough .

 

[FearNoWind]

1/16th inch clearance from barrel to stock is good. The old dollar bill is not enough .

Ditto ....
I'd settle for 1/32 inch but you get the idea.

 

[Broz]

I checked my stock and had a contact point at the tip on the left side.

Let us know if this fixed it please.

 

[bayjoe]

I sure will. I will have to do quite a bit of sanding on my stock to get a 1/32 clearance. I was using the dollar bill.
Probably going to have to wait till the weather gets a little more hospitable

 

[Alaska2006]

+1 for harmonics.
Rifles can be odd creatures, each with its own personality. Find what it likes to eat and feed it a steady diet of that.
I'll usually only dial a rifle in to eat 2 maybe 3 different weight pills and I don't change once I get them dialed in.

I have two 300 win mags, they both eat the Berger 215s and 230s but each rifle likes them prepared a bit different. amazing how two almost identical twin rifles like a bit different load. Either one can eat the others dinner but with less than great results.

 

[Broz]

I stand by Harmonics till proof shots with both bullets are fired. But, the good news is, if you are going long, and want two loads with different bullets, you can easily do this. In the Shooter app, and some others. When you enter the load data you can enter where the zero is from point of aim. Axample: zero height +1" zero windage - .75". Then the app will correct for these when it gives a shooting solution.

Jeff

 

[FearNoWind]

I sure will. I will have to do quite a bit of sanding on my stock to get a 1/32 clearance. I was using the dollar bill.
Probably going to have to wait till the weather gets a little more hospitable

Where you don't have access to a rasp, find a closet rod dowel of rhe correct size you need and some 60 grit sandpaper. That combination can speed up the process. Just remember to finish it down progressively .with 80, 100, 220 grit.