Crossover effect with scopes

L

Lycanthrope

New member
I've always used the Leopold mounts that are windage adjustable in order to align the rifle scope with the bore. In using non adjustable, Weaver style mounts, how detrimental is it to use a lot of windage adjustment in order to zero the rifle? I've heard of the "crossover" effect that will allow groups to creep across the horizontal plane at long yardages. How much of this is a factor up to 500 yards? Any information is appreciated.
 
You shouldn't have to use too much windage adjustment to zero with weaver style mounts, unless the mounts, the mount holes, or the barrel/receiver are misaligned. In case you used some windage adjustment to correct this (moving the reticle out of the optical center in the horizontal plane), the only effect would be less available elevation adjustment. If something is grossly misaligned, this reduction of elevation can be very large, and with a normal 1" tube can make impossible to zero at long ranges.
There is no "crossover" effect that I know of.
 
If its a problem... Millett makes Weaver rings that are more readily windage adjustable than the Leupold style. My preference, after Burris Signatures. ;)
Tom
 
I've got a PSO-type scope mounted on my AK, probably the best example of windage adjustment that can mess you up at long ranges. The scope mounts to the side, and the scope itself actually sits off to the side.

I just finished sighting it in this weekend. I'm going to let you do the math, and maybe you can figure out what you need to know about your application, maybe not. Piece of paper and a quart of coffee should do it.

Using calipers, the dead center of my scope lense sits .6" to the left of the rear sight centerline (left, as in the side of the receiver without the cocking handle).
For a preliminary sight-in, I adjusted the windage to the dead-center of a 25-yd target. At 100yds, the 'windage' was only 2" to the left of center.

Of course, this only being a 7.62x39 AK, I sighted mine in at 100yds and let it be.

I tried it at a 130yd target and 150yd target after I had it zeroed for 100yds. For my purposes, it was dead on, but a pickier shooter may say it was shooting 1/2" or so to the left at 150yds.

Good luck on the math. Use big paper :D .
 
Thanks guys.

Well Yankey, it didn't take a quart or coffee. Just a cold beer and checking the board here cleared things up for me. Your example made sense of what I suspected. I figured a gun with an offset scope that sat 1" left from center of the bore and zeroed at 100 would shoot 1" right windage at 200......2" right at 300......4" right at 400......8" right at 500. Since internal scope adjustments aren't nearly at this magnitude, I thought the effect that I had read about (don't ask me where at this time.....If I could remember, I'd have went back to the text) couldn't be that great.

At any rate, my gun needs around 8-10" of windage adjustment from optical center of the scope to zero up at 100 yards. I'm going with the Burris Signature Z Rings.

Thank you for all of your help.

Oh....any suggestions for Weaver style bases?
 
SFAIK, all the brands are about the same hardness in the alloy. You want to use the thinnest (lowest) bases, lowest mounting of the scope that will clear the barrel, so you can get a good "weld" of your cheek to the stock.

Thinking back to your original question: Some of the earlier, cheaper scopes wouldn't hold the point of aim very well if the reticle was way off from some near-center position. (I'm talking 40 years or so back, okay?) From the way folks talked, they'd sorta drift around in random fashion. Never experienced this, myself.

Art
 
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