Weird windage POI shift when shooting longer ranges (canting the rifle maybe)?

[BCP]

Kind of weird problem but I'll have a good zero at 100 however the windage will be off the further I go out. For example I was .5mil to the left at 300 with no wind. It is most pronounced when shooting at targets that are uphill from me or if I am shooting from a makeshift rest rather than a good bench or prone. Scope seems to be tracking as well, i will dial a lot of elevation and then hold under at 100 and the windage will be consistent so I don't think it is that dialing elevation is causing the windage erector to shift.

The most galling thing is that I don't seem to do it with my AR15s, only the bolt rifles I set up as "precision" rifles.

 

[Citius7]

I shoot one TL3 with a MPA chassis and one with a McMillian stock. It is startling how much cant I put into the rifle moving from one to another so the fit to the shoulder pocket differs and has me putting different degrees of cant. Cant does very bad things out to longer range.

 

[diverdon]

Have you shot a tall target? If not you should do so. Get a bulls eye set up at 100 yards then dial up one mil at a time and shoot one bullet each mil for at least 10 mils. Are your 10 impacts spaced at 3.6 inch intervals directly above the bulls eye?

 

[BCP]

I will try the tall target but it may just be that the rifle chassis doesn't fit me as well as I thought.

 

[Twinsen]

If the optic passes the tall target, get a $30 bubble level. I find they're useful in strange positions and on deceivingly uneven ground. One place I shot from is a slight hill. I had no idea.

 

[vh20]

If the zero is truly good at 100, you'd have to have vertigo to not notice enough cant to put you off 0.5 mil (5-1/2 in!) at 300. A level isn't the answer. If the zero is true, look to either tracking, or more likely, recoil management (you did say the problem exists with more than one rifle).

 

[BCP]

LOL I do have vertigo

Anyways it was a combination of how the scope was mounted and loose nut behind the trigger. Once I corrected those two problems I started hitting everything I aimed at.