Horizontal POI shift in ladder test?

[Wheedle]

I am working up a load for my LR308, built off of a Fulton Armory receiver set and a Criterion 24in 1x10 barrel. Anyway, as charge and velocity increased, POI rose slightly and eventually started shifting right. Also, seemingly odd to me, the last three loads started shifting downward also. Is this horizontal shift anything unusual? My Savage .300WM just doesn't seem to care, piles them all in to one big ragged hole with little POI shift at all, vertical or horizontal.

 

[mike a]

I am working up a load for my LR308, built off of a Fulton Armory receiver set and a Criterion 24in 1x10 barrel. Anyway, as charge and velocity increased, POI rose slightly and eventually started shifting right. Also, seemingly odd to me, the last three loads started shifting downward also. Is this horizontal shift anything unusual? My Savage .300WM just doesn't seem to care, piles them all in to one big ragged hole with little POI shift at all, vertical or horizontal.

At 300 yards I've seem substantial shift horizontally with a .3 grain change. 6 Creed. First time I saw it I thought something broke. Mike

 

[JFrank]

I am working up a load for my LR308, built off of a Fulton Armory receiver set and a Criterion 24in 1x10 barrel. Anyway, as charge and velocity increased, POI rose slightly and eventually started shifting right. Also, seemingly odd to me, the last three loads started shifting downward also. Is this horizontal shift anything unusual? My Savage .300WM just doesn't seem to care, piles them all in to one big ragged hole with little POI shift at all, vertical or horizontal.

Not at all could go any direction, all ya need is a flat spot in volocity

 

[garandman]

I find semi auto is a fickle mistress....

 

[Dusty Stevens]

Did you have wind flags out? You can get all kinds of horizontal shifts with a wind change especially if you take a break between shots

 

[Ned Ludd]

During the harmonic cycle, the barrel [muzzle] does not simply move straight up and down in a perfectly vertical plane. It's more like a slightly flattened figure 8, tilted slightly over toward the right for a right-hand twist barrel. Bullets exiting the bore at the top of the arc of muzzle travel (harmonic cycle) would be expected to have a POI high and to the right, as you observed...totally normal. As noted, the effect of even minor wind can also result in a ladder test with holes that aren't in a perfectly straight vertical pattern. Obviously, these effects are enhanced as the distance increases.

 

[Wheedle]

I find semi auto is a fickle mistress....

True enough. Although this rifle shoots remarkably well with both Federal Gold Match and Georgia Arms match ammo.

 

[Wheedle]

During the harmonic cycle, the barrel [muzzle] does not simply move straight up and down in a perfectly vertical plane. It's more like a slightly flattened figure 8, tilted slightly over toward the right for a right-hand twist barrel. Bullets exiting the bore at the top of the arc of muzzle travel (harmonic cycle) would be expected to have a POI high and to the right, as you observed...totally normal. As noted, the effect of even minor wind can also result in a ladder test with holes that aren't in a perfectly straight vertical pattern. Obviously, these effects are enhanced as the distance increases.

Although I really know little about barrel harmonics, that is kind of where my mind was going. Didn't expect it to do a figure-8 though. interesting...

 

[Ned Ludd]

The "figure 8" is somewhat anecdotal...I've never actually seen super-slo-mo images of muzzle movement during the harmonic cycle, and I'm not sure how trustworthy they would be anyhow, with everything else that is going on with the rifle during the recoil impulse. Nonetheless, I have observed the slight tilt to the right for POI in addition to the upward travel on a number of ladder tests, where wind was unlikely to be the cause. I wouldn't say it's "abnormal".