Rifle Scopes Canted reticle effect?

[m1ajunkie]

Shooting yesterday confirmed some data from a previous range trip where I got some windage data that didn't match what I thought it should be.

Shooting my .308 ar on a very calm day, if anything wind was blowing right to left but at most 3-5mph. However, I was having to add in left windage from 300-675yds.

300yds- .75moa left
400yds- .75moa left
500yds- .75moa left
600yds- 1 moa left (this should really be about 1.5moa confirmed later in the day)
650yds- 2 moa left
675yds- 2.25 moa left

Two different range days gave the same results as far as windage. Same conditions one month apart.

I am looking at my reticle today and it seems it is rotated counter clock wise a tiny bit. When I mounted the scope I used a level on top of the elevation cap and one on the rail to level. The level indicated it was between 0 and .2 degrees off, it was tough to keep it leveled while tightening the mount.

Can a slight counter clock wise cant lead to these unexplained but repeatable windage adjustments? I need to get an anti cant level but I feel I was holding the rifle as level as possible.

I will be shooting a match sat the 16th at this same range and I am just planning to dial in the dope I have for both wind and elevation as those seem solid.

Thinking this through in my head, it seems the counter clock wise cant would mean I would need right windage. Any other ideas about why my windage is consistantly hitting to the right at the extended ranges when conditions are so calm?

 

[dcjs]

Re: Canted reticle effect?

Assuming you are using holdover (if the turrets are square and you dial, a canted reticle doesn't matter), the windage deviation is simply the sine of the cant angle times the amount of holdover. A reticle that is canted counterclockwise will produce hits to the left of the point of aim.

 

[m1ajunkie]

Re: Canted reticle effect?

I have decided that the scope and reticle are level. I verified with a string hanging and placing a level on top of the elevation knob.

At this point I feel like it is the conditions on this range which give me the windage change, and when I shoot the match I am simply going to trust my data and dail what has worked the previous two times.

The targets at 600, 650, and 675 are back in a wooded area while the targets from 100-500 are in an open field. I am thinkng the change from the field to the wooded area is causing the shift, and the data shows the change occuring between 500- 600yds. Does this sound plausible?

I don't have access to any other 600+yd range to verify this theory, but I would like to shoot some matches here in the SE and need to know what to do with my dope. I am thinking when I shoot at ranges that aren't the one where I am experiencing the windage change, I will simply dial zero windage and see what happens.

 

[Guest]

Re: Canted reticle effect?

for one I would never trust leveling the scope with the adjustment caps. I use an exd device from brownells, this levels the gun and allows you to see through the scope. I have a window on the neighbors house that I have verified is level at least one side of the frame is. with the gun leveled with the EXD device I line up the reticle to this frame. if the problem is your scope is adding in windage as it tracks I would think this would also cause you to shoot low as well.

the best way to check is draw and upside down T on poster board, make it exactly perpendicular. aim at the base of the T with your base zero. next dial in 20 MOA or how many ever MOA you think is the most you will use. fire another group, the group should be centered on the line all beit how many MOA you dialed up from the base.