Rifle Scopes Shots to one side when hold overs used?

[FromMyColdDeadHand]

I have a Premier 3-15 Mil-dot on a JP 18inch upper in a Larue SPR Mount. Just getting used to using a higherpower scope for long range shooting. I was working my come-ups and hold overs for different ranges and I noticed that if I used my 100 yard zero and held over for 400 yard shots, my rounds impacted 6-8 inches to the right. If I dial in my dope and shoot POA/POI it is right where it should be. Does this mean I have a cant or something in the system somewhere?

It happened a few times, and always in the same direction.

Thanks

 

[dcjs]

Re: Shots to one side when hold overs used?

This sounds kind of odd. Looking at it systematically, if you dial elevation and POI is spot on, this means that your scope is mounted level (using the turrets as a reference). Now if POI moves to the side when you hold instead of dialing, this would suggest that the reticle is canted. But, for the amount of error you are quoting, you would need something like 10°-15° of cant in your reticle (I could tell more exactly if I knew your dope, how much holdover were you using for your 400 yard shots?), and this would JUMP at you when looking through the scope for the very first time. About 1° of cant may be visible, and 3° will be noticeable right away.
Considering this, my first guess would be changing wind conditions or some other error. If you can't see the reticle is canted with your bare eye, cant simply cannot produce an error of this magnitude.

 

[TXCOWDOC]

Re: Shots to one side when hold overs used?

2 comments:
Vertical crosshair not true i.e. plumb. Solution- hang a plumb bob on a string 70-100 yds out your back door and with your rifle level check your crosshair. You ought to be able to hide the string perfectly top and bottom. Tough to do on a windy day. Or take a 48" piece of cardboard and nail it to the back stop. Take your carpenter's level and strike a verticle line in heavy black marker- same effect.
2. Your rifle is not plumb when you shoot. Once your reticle is true, make sure you have a reticle level mounted to your tube. 15 deg pf cant starts to matter as hold over (distance) increase-

 

[chad3]

Re: Shots to one side when hold overs used?

Reticle is off true but the knobs work so coming up will shoot right and hold overs will mess you up.
Chad

 

[Straight Shooter]

Re: Shots to one side when hold overs used?

I really like Davids explanation but there could be another cause if the situation was the other way around. If you are near the edge of the available travel in your scope the erector will be pushed by the scope tube as well as the turret causing the tracking to go askew. You can detect this by leveling up your rifle and using a boresighter run the turrets through the scenario that caused the sideways shift and see what the tracking is actually doing.

Here is the premise behind my theory. A scope tube is round and assuming the erector is perfectly centered it will have the max elevation available. My theoretical model is based on a scope with 100 MOA total travel available so from center it should move 50 MOA up or down from center.

Here is what happens. in Scenario #1 Run the wind-age to the left 40 MOA. You now only have say 20 MOA elevation left going up before the erector hit the tube and loses contact with the turret contact point. When it loses contact it will start to follow the arc of the tube and cause windage changes when the elevation is changed. The erector is held in contact with the return springs and the springs will just compress and you can't feel it but will show up as what you are describing.

Scenario #2
Now starting from center run the windage screw clockwise moving the POI to the right the same 40 MOA. Now you still have 20 MOA available up or done but now when you hit the end of the available travel it will be trapped by the turret contactor and the wall of the scope. It will bind up and you will feel it and you will know you are out of travel.

Being you said you are using holdovers rather than clicking your reticle is severly canted.

 

[FromMyColdDeadHand]

Re: Shots to one side when hold overs used?

Thanks everyone for the insights. Next time I'm at the range I'll be sure to take my rail level and small level for the scope turrets and take some careful shots with these in mind to make sure I'm not canting anything. I'll also recheck the reticle, I plumbed it at less than 25 yards, so maybe there is something there. For hold overs and MIL dial ins, I was zero'd at 100 and I was using 2.3-2.4 Mil changes.

 

[Graham]

Re: Shots to one side when hold overs used?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: FromMyColdDeadHa</div><div class="ubbcode-body">It happened a few times, and always in the same direction.
</div></div>If it happened at 400, and only a few times, then it's probably not your scope it's your trigger pull.

 

[FromMyColdDeadHand]

Re: Shots to one side when hold overs used?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: FromMyColdDeadHa</div><div class="ubbcode-body">It happened a few times, and always in the same direction.
</div></div>If it happened at 400, and only a few times, then it's probably not your scope it's your trigger pull. </div></div>

More likely the trigger puller.. I meant to say that the few times, 3-4, I used the hold over at this range, they always where to the right. Shooting IPSC steel sillohottes (damn that is hard to spell?) I still got hits, it was just when we were shooting paper that I was able to quantify it better.