90 degree shooting with optic

[D_]

Whst should I expect?

I have an Elcan SpectreDR zerod at 100m. I tried shooting 90 degrees with handle towards right and was hitting low and left by about two to three inches each way. Nice grouping as well so that's where it was hitting.

Is this to be expected or is there something wrong? I understand gravity is always down and the reticle is turned. I was expecting poa is poi at that distance. I must be wrong. Kind of a rifle noob. Is the movement height over bore being turned?

School me please.

 

[Sosa]

Nope that is to be expected. If you try turning your rifle 90 in the other direction you will start to notice a pattern emerge. It takes most people a while to discover this usually.

Has to do with the fact that the lines between the scope and the bore are not parallel, even when zeroed for a specific distance.

 

[Ganderite]

I have tested three rifles and then shot them sideways. All of them shot low right. All I do is pick a new aiming mark that puts the hits in the middle.

I will leave it to others to explain why the shots don't go to POA. I don't like to argue with the gun and bullets holes.

Once I know where to aim, it is easy to hit the bull.

 

[scott585]

the rifle when turned now has a few issues, its vertical zero is for 0 yards, not 100, so by 100 yards, it has some drop added to it. combine this with the new horizontal zero being somewhere between 1 and <100 yards and it will be low (bore parallel to LOS) and to the left (its in a horizontal "climb" to beat gravity and there is no horizontal gravity)

if you shot at a 25 yard target with no changes you would get low (not as much) and to the right, and if you shot a 300 yard target with no other changes you would get much lower and much further to the left

 

[Long]

As already discussed when your shooting any rifle canted there are two vital aspects of your sighting system which have been altered.
First obviously is your elevation. Your zero at 100m or whatever range has a certain amount of rise in the bullet's trajectory incorporated into it to account for the effect of gravity and your sights height above bore. If you were to cant your rifle 90 degrees you would end up hitting low due to now having like previously mentioned basically a zero meter zero.
The second aspect is linked to the first. When you cant the rifle 90 degrees you take your sights elevation and no longer apply them to the bullet's elevation trajectory but rather to the windage of your sighting system. This is what causes the POI to be either left or right of your POA depending on if your canting the rifle to the left or the right.

I have one AR 15 with an ACOG mounted and sighted in such that when shot canted from a position such as roll over prone at 100m it will be 4 inches low and 4 inches left or right depending on which way I have rolled the gun. Similarly I have a .223 bolt gun with a mil reticule scope with a 100m zero and at any distance the canted 100m zero is 1 mil low and 1 mil left or right again depending on which way the gun is rolled.