[JRWhit]

I was going through workup on a 220gn rn interlock using retumbo powder.
I anticipated point of impact to be low as my rifle is sighted in for 180gn bullet.
What has thrown me off is that all three groups of five are hitting 2.5in low and 3.2in left of point of aim. I saved 5 180gn loads for comparison and fired them last. All 5 grouped at point of aim. This throws out the idea that it's from flinching even though I'll admit that the punch brings back bad habits. The point of impact hitting that far left doesn't make sense to me. Does anyone know what causes this? Will further work up bring it back in?

[rcmodel]

Barrel harmonics.

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

It could be up, down, or sideways either way, but it won't hardly ever be the same when switching bullets.

rc

[gspn]

Crazy isnt it? Shooting factory loads one time i switched bullet weits of the same type of cartridge...and i shot 6 inches to the right. Fully expected vertical...but was shocked to see all new groups that far to the right.

It reinforced the already ingrained habit of re-zeroing my hunring rifle whenever i make any type of change.

[JRWhit]

Wow,thats very interesting. I have seen a super slow motion video of barrel contortion when fired but I had never thought of it as taking place while the bullet is still traveling in the barrel. Thank you for the link.