Back when I was writing Sightron sent me two scopes. One had a zero shift when changing power so I sent it back and got a replacement.

I have been shooting 10 rounds offhand at 100 yards using a .223 every week and noticed my 100 groups were centered to the left while shooting at 4X. I had zeroed at 200 yards at 14X. So yesterday I decided to conduct a little experiment: I shot one shot at 200 at 14x, then dialed down to 4x. Repeated this twice, so I had two three shot groups.

The 4X group was 4 inches left at 200 yards. Both groups were under 1 moa.

I see Sightron is now selling some pretty expensive scopes; mine are older scopes, but still, I don't recall seeing a zero shift with other scope brands. The other Sightron is on my Ruger No1 .204; need to run the same test.

Anyone have similar experiences?

That's interesting, esp. since RIP has included Sightron in the brands he has not been able to destroy on his 458WMs.

I presume the problem comes from having the reticle in the 'second focal plane', where power changes occur ahead of the reticle and any slop in the mechanism will move the zero. Manufacturers assure us this can't happen any more - but they would, wouldn't they?

While no way as secure as the old reticle-movement system, modern variables with the reticle in the 'first focal plane', which enlarge as the power is turned up, should avoid this problem at least until the erector spring malfunctions.

This is nothing really new, and since I've referenced Formid from other foums (the USDOD guy who tests ammo, optics, etc for a living) I'll do so again. He has "wrecked" every scope brand made, period, but a very small handful are tougher than all the rest.

Nightforce is the clear winner in toughness, reliability, return to zero
Fixed SWFA's, the 3-9x, and 5-20 are great
Bushnell LRHS 3-12x, 4.5-18x great as well
Vortex Razor Gen2
S&B (not sure which specific models)

Nothing else has held up worth a crap in his world, but he admittedly shoots more than anyone else does in 20 lifetimes.

JG, I thought you said S&B were rubbish a while back.

quote:

Originally posted by sambarman338:
JG, I thought you said S&B were rubbish a while back.

No, I said some of their pencil thin reticles are/were rubbish and useless.

OK, thanks for that.

Most scopes have a shift but usually at only the extreme range in their adjustment.

Try this, recenter the scope in its adjustment range. Retorque rings to 15 inch pounds.

Now re zero adjusting windage first (windage should always be adjusted first on scopes with leaf springs holding the erector tube assembly).
If this doesnt work sell it cheap to someone you dont like.

Buy a Swarovski.

I tend to adjust the windage first, too, Abbispa, but mainly for aesthetic reasons.

Is there a mechanical reason?

To stop the spring(s) chattering on the outer tube, I'd have thought a combination of windage and elevation moved incrementally might be best.

On the matter of zero changing between different powers, however, I would not have thought the turret adjustments had much to do with it. The problem arises because the second-focal-plane reticle is back near the ocular and the target picture it's imposed on has come through the erector tube first.

The power scroll is part of the erector set (magnification was traditionally raised by moving the erector lenses forward in the scope) and if the housing of these lenses maintains perfect concentricity as they move, then zero will stay put. If not, or if any looseness develops in the mechanism, the bullet impact will change at different magnifications.

As I explained earlier, the obvious answer is get a scope with a first-focal-plane reticle, which is either connected to the front of the erector set or, in the old reticle-movement scopes, a separate assembly ahead of it. Either way, FFP reticles unite with the target picture and the relationship cannot be disturbed by changing power. Parallax may still be a problem, of course.