Tim Finley's 'Crossover' Article-Optical centre?

[derek austin]

After reading the esteemed Mr F's recent article in the mags, I thought I'd check over my new AA MPR/Lightstream set up.

As per, I optically centred the windage of the scope (90 out of 180 clicks L-R total), and shot at 10 yds, pretty much on it, a tad right. Then tried at 25yds (max in my garden), and shooting a long way off left.

"Aha" me thinks, "time to do this here shimming he mentions". Down to model shop, sheet of brass as per instructions.

Now then, brain starts to hurts a bit - I think that if it's shooting left, then I should pack the shims 'alongside' but 'under' the dovetail of the mount on the right, rear mount?? Unfortunately Mr F doesn't make this clear in his article...

ie should the shim(s) go on the opposite side to the 'misfire' - shooting left, pack on right? - and presumably only on the rear mount, not both?

So, two little bits of shim end up on rear right mount, and POI at 25 yds moves R as required..

Anyhow, having got it shooting straight at 10 and 25, albeit with a bit more help from the windage turret (which really I shouldn't need), I get down the club and my first pot at a 40+ yarder goes a good 2" left (no wind, BTW, and I'm not that bad a shot), necessitating a good old fashioned crank of maybe 10 clicks to the right to bring it straight.

Now I'm totally confused.

(Don't have this problem with my Daystate/Zeiss BTW.)

All help gratefully received.

Derek

[BigAl]

The scoe should be about optically centered when the turrets are at the mid points but that is not allways the case to check the optical center you need to mount the scope in some v blocks Use an old shoebox with a couple of v's cut in the sides lay the scope in the blocks and set it up so that you have some sort of aiming point for the cross hairs. Rotate the scope through 360 degrees the crosws should make a oval / circle around the aming mark. Adjust the turrets untill the circle is as small as possible the scope will now be truly optically centerd.

HTH

Al

[derek austin]

Thanks for that suggestion - however, still not clear as to how exactly to shim the mounts, ie on which side?

Derek

[peejay]

Just spent the afternoon setting up an FX 3-12x44 on a 177 verminator, once the scope is optically centered (you could try rotating it in the mounts as a v block, only if the gun is firmly monted,) shim so that you have the same deflection (as viewed through the scope using the mil dots as measurement) at both near and far targets. If confused as to where to put the shim try putting several on one mount and work it out from there by noting the results. It helps to write it down. When deflection is the same, then adjust the windage turret to centre the vertical (y axis) cross hair on the hit point. Then you have many happy hours zeroing the distances on the top turret. Hope this helps.


FX verminator .177
FX Storm .22

[theboymike]

You're approach to shim placement seems correct, although shimming mounts isn't really the ideal solution.

I had a problem with crossover on my S410 which was eventually solved with a set of B-Square adjustable mounts and a good setup using a spirit level and a plumb bob. Now everything is splendid

[derek austin]

A mate mentioned the B squares, but I don't think you can get them in 1" Low?

Derek

[ross H]

A mate mentioned the B squares, but I don't think you can get them in 1" Low?

Derek

think you will get them in medium though, you will be hard pushed to use low mounts on a lightstream i would think

[flims]

The scoe should be about optically centered when the turrets are at the mid points but that is not allways the case to check the optical center you need to mount the scope in some v blocks Use an old shoebox with a couple of v's cut in the sides lay the scope in the blocks and set it up so that you have some sort of aiming point for the cross hairs. Rotate the scope through 360 degrees the crosws should make a oval / circle around the aming mark. Adjust the turrets untill the circle is as small as possible the scope will now be truly optically centerd.

HTH

Al

Some also call this process "Spinning the scope" i had read an article about it with some photos but forgot how its done properly. Do you have a link to it so i can see the steps carefully. I want to check if my Leupold Mk 4 is optically centered.

[BigAl]

Im sorry I dont have any articles on how to do optical centering I got the information from an american book on sniping that I borrowed from a friend at the rufle club. the best approach is to keep the movements small so that if you go too far there is not so much to go back to find the correct position.

Alan