Point of Impact Shift (Left/Right)

[MattM]

I went out shooting today. The rifle is a Bergara in 300 WM and I was shooting at 100 yards doing load development. The rifle has a 6-24x50 Vortex HST scope. This scope was previously on a 7mm-08 and shot with no problems. Today, the first group was 1.5" to the left of the bullseye. The next 5 groups were 2" to the right with no changes to the turrets. The vertical barely changed as the powder charge increased (0.5g/group). I adjusted the windage 2 MOA to get the group back on center. The next 2 groups were on center and then it moved back 1.5" to the left of the bullseye for the final 2 groups.

I came home and checked the torque on all the screws for the base, rings and action screws and everything was still tight. My thought on this...there is something wrong internally with the scope and needs to be sent in for repair. Any thoughts on this are appreciated as I just want to make sure I have this narrowed down correctly. If it means anything, the groups were ranged in size from just under 1/2" to just over an 1" and the vertical changed with the powder increases, which I expected with doing powder load development. Thank you in advance!

 

[darkangel_r2]

Not necessarily. My sav 12 lrp has a primarily horizontal POI shift in barrel vibration pattern. 10 charge levels dead flat just moved to a left or right POI cluster. Pick a charge level with acceptable group size and SD numbers in the middle of one of the stable POI clusters or get your barrel indexed to a vertical vibration profile.

 

[Dusty Stevens]

How bout them windflags?

 

[M-61]

Any thoughts you ask? Yup.
First thing I would have done is get by buddy to shoot it. We happen to shoot the same as each other which is a gift. See what he gets.
Then I would have tried any other scope that I had. What happens?
Put another scope on and see what it does.
You have narrowed it down correctly.
In all the scopes I've owned I've had only one in which the POI changed. Doesn't mean you don't have one also.
Now the sorrow. Many decades ago I had a beautiful blonde stocked Sako in 220 Swift.
Could not get a consistent group. 3 nice and then 2 way off. And every version of that.
Sold the rifle. As I found out the problem was the scope. I'm still pissed after all this time.

 

[4xforfun]

How bout them windflags?

I agree.....but 3+ inch shift with a 300 WM at 100 yards?? That right there is a PILE of wind.,

 

[MattM]

There was no wind that I could feel. I’ll get my buddy to shoot it as soon as I can…I work graves and he’s on days so schedules don’t always line up.

 

[M-61]

How bout them windflags?

Not a chance unless he had trouble being blown off the bench.

 

[Coyotefurharvester]

Vortex has a good warranty, use it.

 

[JoeDuke]

Try a different scope.

 

[Louisiana Shooter]

^ this first before calling anyone.

 

[Fast14riot]

My family has had 4 Vortex scopes go bad, including a HST. I won't touch them with a 10 foot pole.

 

[22BRGUY]

Not saying you are or aren't, but consistent cheek weld and or trigger finger not centered on trigger can throw a bullet to a greater or lesser extent at least I found it did for me from time to time. Also a scope level made a difference.

 

[gunsandgunsmithing]

I usually do as Dusty and start with wind but I agree with others that that's too much at 100 in very light conditions. Before doing anything else, if you haven't done so, go over every screw and look for something simple before jumping off the bridge. It's usually something like that. Not a bad idea to change scopes. That really narrows things down in a hurry and you might find the problem while swapping them. Pay close attention to the front base screw. Loosen the back screw on the front base first and see if it wiggles with just the front screw. Common for that screw to be too long and it bottoms out on the bbl threads before tightening the base. It can feel tight because it's bottomed out before it actually tightens the base. Again, simple stuff first, then dig deeper. If you don't find an obvious problem, swap scopes. Go from there before calling anybody. Then call a buddy to shoot it. Still bad...then call a smith if swapping scopes didn't pinpoint things.

 

[K22]

After checking all the screws / mounts, I'm in the change scope crowd and see what happens.

Will firmly securing the rifle on the bench and moving the turrets tracking the movement on a scale at 100 yards reveal any damage or loose internals? I seem to remember reading something about this procedure many years ago but forgot the details. Does this have validity? Perhaps you guys can chime in on it.

 

[Old Navy]

My Golden Eagle was doing the same thing. I found the eye piece was loose. I sent it to Vortex. They repaired it in three days and shipped it back along with a letter explaining what they did. It shot a perfect tracking square. Great service. You might want to check your for play.

 

[MattM]

Thank you everyone for the insight. I’m going to switch the scope from another rifle and shoot it. Hoping it’s something simpler to fix.

 

[22BRGUY]

Thank you everyone for the insight. I’m going to switch the scope from another rifle and shoot it. Hoping it’s something simpler to fix.

please keep us posted on what you find out
Best Wishes

 

[rwj]

Not saying you are or aren't, but consistent cheek weld and or trigger finger not centered on trigger can throw a bullet to a greater or lesser extent at least I found it did for me from time to time. Also a scope level made a difference.

Improper parallax adjustment will also contribute to the problem…

 

[Ned Ludd]

The center points of groups can certainly move around the POA during the load development process. However, the amount of movement you describe seems excessive for 100 yds, even if the rifle has a pencil barrel, which I don't think your rifle does. As has been mentioned, there are a host of potential causes including shooter error, something loose on the rifle, parallax issues, etc.

I would suggest a simple test to determine whether you might be able to eliminate the increasing charge weight (i.e. load development) as a potential source of the POI movement. Load up a few more rounds of each of the two charge weights that caused the greatest/most obvious POI shift in your previous outing. Rather than shooting them as groups, just go back and forth between the two loads using single shots. If the charge weight itself is causing the POI shift, you will see the individual shots go back and forth ~3" across the target face. It shouldn't take more than a couple or three shots at each charge weight to convince you whether the changing charge weight was the culprit. If the POI of the individual shots do not behave as the groups did before (i.e. move 3" L/R), then at least you will have eliminated the charge weight/load development process as the source of POI change.

If nothing is obviously "loose" on the rifle, it is not uncommon with this type of issue to have to carry out a number of tests sequentially, isolating a single variable at a time in order to identify the probable cause. Basically, you may end up having to rule out potential causes one at a time. It can be painful, but worth the effort if you are able to isolate [and correct] the underlying issue.

 

[drop_point]

Is this your first big magnum?