Tell me if my logic is correct on the following:

It is known that to raise the point of impact with iron sites, one either raises the rear sight or lowers the front site.

When bore sighting a scope, if the bore is lower than where the crosshairs are, one turns the adjustment dial DOWN which physically lowers the cross hairs and brings the impact point up.

Now the question, will ring height change the impact point of a scope? It would seem to me, that if one ran out of scope adjustment in the up direction, lower rings would bring the impact point up.

I spoke with someone today who I would consider to be knowledgeable, who said ring height wouldn't make a difference. Maybe he's right but it doesn't make sense to me. He also said there could be wide variation in the adjustment limitations between scopes even of the same type from the same manufacturer which I suppose could be true.

The background on this is a CZ 550 Safari Magnum in 458 Lott that I wish to have 2 sets of rings with 2 scopes each sighted in for a different weight of bullet. I'm using Talley quick detach rings. The Leupold VX I 2-7X I'm using for 350 grain bullets is working fine. I've tried a Leupold VX II 2-7X and a VX II 3-9X with 500 grain bullets and in each case they shoot about 6 inches low at 100 yds. at the maximum scope height adjustment.

I'm more than happy to try different quick detach rings or even a different scope if it will solve my problem.

A higher base on the rear will give you more up adjustment, If you raise the entire scope you are lowering the bore needing more up adjustment. The raise on the rear will tilt the scope down. The reason a gun sighted at 100yards say will hit about the same distance low at 25 that the center of your scope is from the center of your bore,ussually about an 1 inch or 1 1/2. Clear as mud, I hope that explained it.

Didn't I agonize over this last week?

When my .223 900 yard range rifle ran out of klicks with a 24x fixed scope, a mate with a lathe and or milling mechine (all Dutch to me)
just sloped the underside of the mounts a couple or few degrees, down at the front (I think) and Bob's your Uncle.

Same trick may fix a wonky CZ. Forget up and down, you need slope.

I thought the silly prick would then run me out of adjustment at 200 yards, but no, a real fluke.

Ohio:

I'm not sure about the ring ht question, I don't think it will make any significant difference.

The real question is why you would even consider using two scopes for different bullet wts ON THE SAME GUN. This is exponentially worse than carrying 2 types of bullets (you always have the wrong type in the chamber when the trophy animal appears).

Assuming you want to go foward with this insanity AND use the same scopes (30mm scopes have more adjustment range), you have two choices, mill the bases or rings where there is a slope down or forward or shim the rear ring. There is at least one company that makes shims or you can use a piece of beer can on the rear rings but it would tend to bind your scope, and on a big kicker this might (I say might, I'm just guessing) lead to early scope failure.

The 30 mm scope is a good suggestion.

As far as I can see, there is no way to shim Talley quick detach rings that fit on a 19 mm dovetail or I would have tried that.

As far as the logic of 2 scopes for the same gun goes:

1. The scopes would be enough different that I could tell just by looking which was which.

2. Two scopes would give me a backup in case one quite working while on a trip.

3. I would only be carrying one type of ammunition while hunting with a given scope. The one for the 500 gr. bullets would be intended for the likes of buffalo and giraffe and the one for the 350 gr. bullets for everything else.

From the answers I've gotten, I believe the optical axis, so to speak, of the scope has a lot more to do with impact point than ring height.

I go with Gatogordo on this one. Somehow you get the wrong ammo. To me it's about the same situation as those using a pointed bullet for their first shot in a 30-30 for example. Yes you can see the difference. But it is also like having a pet rattlesnake it seems to find it's way where it doesnt belong. Set up two rifles---then you really have a back up.

I'm sitting here looking at a pair of Talley QD rings on a 1.75x6 Leupie. I can't see any reason they can't be shimmed like any other ring but admittedly haven't tried it. The obvious answer is to machine or file, if you're good, the bases to deliver an downslope towards the front.

Whatever scope set up you wind up with, I urge you to consider 1) use one scope for both loads, either using "come ups" for the heavier load, which you are likely to use much less often, or simply hold over and 2)carry a second scope set up the same way. As far as the "hunting with one type of ammo" that's a mistake and is a poor plan unless you are specifically hunting only one species, say, buffalo and absolutely would not shoot something else. Most hunters are not that specific. Otherwise, It is quite likely you'll run into some trophy plains game while hunting buffalo or vice versa. If you're going to take two types on a trip (another mistake IMO) then by all means carry a few of both types with you while hunting. I'd solve the whole problem by using Nosler Partitions, A Frames, Barnes or similar for everything.

Gatogordo, the issue is that he is using Talley bases on a dovetail type mount. You can't shim those!

You might get away with a low mount up front, and a medium height on the back though......

don't know what kind of bind that puts your scope in, but if the difference isn't that severe (which it might be) I don't suppose it is any different than shimming.

If you called Dave at Talley he could probably give you some insight.

Yes, that is the problem, I see no way to shim Talley mounts. Also, rings for the CZ 550 only come in one height. In addition, with a gun with recoil like a 458 Lott, I think different ring heights would put too much stress on the scope tube.

In addition, I did talk to Dave Talley who was very nice and said I could send the rings back if they didn't work. His suggestion was to put the 3-9X scope in the other rings to see if they worked with those. It is a good suggestion but I've done enough mounting and unmounting scopes on this gun so I'm not doing that.

What would work would be something like Burris Signature rings with the eccentric plastic inserts but I don't think they make anything for the CZ 550 in a quick detach version. I could also use a scope with a better range of elevation adjustment if there is one that would hold up.

I may just have to be satisfied with using the scope for load workup (it's a least on paper if I use a big target) and iron sites if and when I hunt the big stuff.

quote:

Originally posted by Grumulkin:
Now the question, will ring height change the impact point of a scope?

Yes.

Higher rings also increae MPBR.

That's why Burris makes Signature rings !!! With the offset bushing set, you can pick up about 40 MOA if needed by using different bushing combos. I won't use anything but Signature rings.