From my 257 Roberts Ackley improved I shot 72 gr, 87 gr, and 110 gr.

The group of 110 gr holes was centered 2.5" to the left of the bullseye.

What would cause this?

Hello Clark,

The barrel has harmonics like a rope when the gun is fired. The harmonics move in both horizontal and vertical planes. I suspect that the barrel harmonics are such that the heavy bullets exit the muzzle when it is pointing more to the left than the light bullets. Nothing to worry about, but good to know. That's why you always need to zero for that particular load.

Regards, Bill

I agree with Bill. In addition, there could be some uneven bedding which shows up with the 110's that might not show up with the others. You might want to check that out, but most rifles will group to a different point of impact with different weight bullets. It's a rare one that doesn't, and 2.5" of difference is not uncommon.

finger on trigger pulled to right?


[ 11-22-2002, 21:15: Message edited by: John Y Cannuck ]

Max loads with 200gr BT's from my .338Winmag do this. 71gr. of H4350 and it's 2.5" high and center. Jump to the 73gr. max load and it's 3.5" hight and 3.5" right.

Are you by chance a southpaw?

I am right handed.
The rifle was right on with 72 and 87 before the 110 gr.
I shot the 110 with the ecentric point on top, the same as the lighter bullets.
After the 110, the rifle was still right on for the 72 gr.

The rifle's recoil arc has the most to do with this.

The rifle doesn't recoil exactly straight up, it will arc slightly to one side or the other.

If the bullet you're firing has more barrel time (heavier bullets usually have more barrel time) it will exit the muzzle at a later point in the recoil arc. The liklihood that this point would be left or right of center is pretty good. The rifle usually arcs away from the barrel's twist rate because it is opposing the bullet's direction of twist.

If you fire the rifle from the standing position, you may notice a completely different POI again. This is due again to the recoil arc, which is altered to some degree when the shooter changes positions.

Take care,

Dan Newberry
green 788

It is very rare for any rifle to place all weight bullets to the same point of impact. It is normal and to be expected. Experience reloading and time will show the novice reloader how and why a rifle shoots a certain weight bullet. You must readjust your thinking when it comes to reloading and how barrel harmonice work on a rifle. No two rifles will shoot the same no matter how perfect they are made.

Because the bullet wanted to get to the other side of the target?

The 6.5X555 Swede is the only one that will place bullets of different weights in the "same" place. After more than a century... nobody has figured out why this is so. It just is.

And that's enough for me.

Clark,
My bet goes to the right hand twist of the rifling. The heavier, slower bullets would twist the rifle more throwing the bullets to the left.

PaulS

Clark -- To have two bullets of differing weight, same caliber, printing at the same point of impact on the target, would be very rare indeed. The variables are so great, it is nearly impossible. Even you will group the same bullet at slightly differing points on the target on different days. Those groups of different weight bullets, same caliber, may be several inchs apart on the target. I have only one rifle, and I shoot a dozen of my own and 20 others each year, that will do it. It is a .340 Wby, and it will put different weight bullets in virtually the same group on the target, those being 225 gr. and 250 grain North Forks. This is my experience, for what it is worth. Good shooting.

I had a .280 rem. in a m77 ruger that would always throw the 165 grain roundnose cor-loks down and to the right alittle from where the 150 grain spitzer cor-loks would land.

OK, here goes my SWAG (Scientific Wild A@@ Guess)

The barrel twist is right hand, and the barrel vibrates at the same frequency every time you shoot those bullets. The bullets must be leaving the barrel when it (barrel) is moving left, so the shots hit left. Probably wrong, but that is how all of my SWAGs end up...

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