Scope Alignment Question...

[jp.cherokee]

Hi All,
I just put a new Burris Fullfield II 3-9x40 scope on my sons 22 rimfire Walther G22. The windage is fine but it shoots about 8-inches LOW at about 40 feet . I have switched the front to rear mount and it went from 2-inches low to about 8-inches low. Lets hear some options. If I shim it do I shim the front or rear? I think I would shim the rear up???
TIA
Sean

[proraptor]

why not just adjust the scope?

[jp.cherokee]

why not just adjust the scope?

Tried that. The elevation adjustment does not have that much range, it maxs out. Not good for the scope.

[maxicon]

All scope sighting problems are basic physics and mechanical tolerances, so let's take a look at your setup.

40 feet (13 yards) isn't that far for a scope, even on a .22, and with the scope that high off the bore axis, I'd expect there to be some offset. 2 inches at 40 feet is roughly 15 MOA, and that's a lot of adjustment for a scope.

1 inch is about 1 MOA at 100 yard, so (100 yards)/(13 yards) tells us that 1 inch is 7.7 MOA at 13 yards, which tells us that 2 inches is 15.4 MOA at 13 yards.

Figure if your scope was perfectly aligned with the bore and you shot a target at point-blank range, the hole would be off by the height of the scope's center above the bore's center (looks like 3+ inches from the pic).

If the bullet's trajectory is flat (which it essentially is at short distances), you'll need to have the scope pointed down (or barrel pointed up) to get the aiming point and bullet trajectory aligned, and then as you move further back or forward, you'll be off again. At longer ranges, you have to add in the drop in bullet trajectory from gravity, but let's not complicate stuff too much for starters.

So, you should be able to sight in the scope, but with the high scope axis, you may be running out of scope adjustment at short ranges.

However, because your POI shifts a lot when you swap the rings, it sounds like either the rings aren't the same height or one's not seating correctly, since the height shouldn't change much as you switch rings front to back.

If you have a caliper, you can measure from where the ring/rail seating surface to the bottom of the scope seating surface. I'd also inspect the bottom of the rings for any machining problems, and seat them onto the rail, both with and without the crossbolt, to see if it's seating firm and flush against the rail, with no wobble or rocking.

With the scope that high off the bore axis, you should be able to zero once everything's level, but as your range changes, your correction will change a good bit with a .22.

The Burris docs should list the maximum amount of correction available, as well. I'd be surprised if it can adjust 15 MOA, but it's possible.

[xenophobe]

Buy better rings.

[jp.cherokee]

Buy better rings.

I'm pretty new to scope's and rings, but the rings are Leupold PRW High Rings, No. 54150. I bought the high rings for my OLL so I could get above the front sight, but I am using this scope on the 22 rimrife for now. The scope is pretty high above the bore site, and for the short distance, 40-feet (my back yard length for bunnies) I guess I might have to shim the rear up to bring the front down... Comments???
TIA
Sean

[Technical Ted]

I'm pretty new to scope's and rings, but the rings are Leupold PRW High Rings, No. 54150. The scope is pretty high above the bore site, and for the short distance, 40-feet (my back yard length for bunnies) I guess I might have to shim the rear up to bring the front down... Comments???

You could've gone with low rings. The front sight base won't pose a field of view problem with a scope over 3X.

[jp.cherokee]

You could've gone with low rings. The front sight base won't pose a field of view problem with a scope over 3X.

Hi Tech Ted, hope your having a good weekend. I just edited my last post.
Sean

[Technical Ted]

Hi Tech Ted, hope your having a good weekend. I just edited my last post.
Sean

Well...the separation of line of sight through the scope from the bore centerline looks like it's about 4". I forget the height difference between the High and Low rings, but the low rings will drop you about a 1/4".

Even 1/4" might eek out enough elevation so that you're not completely bottomed out.

[Fjold]

You can shim the rear mount up but the underlying problem is still there, the scope is so high above the bore line that you are always going to be shooting low at distances less than 100 - 150 yards or so.

If you shim the rear mount up to get the gun sighted in at 13 yards it will hit low at distances shorter than that and probably be sighted in 4 feet high at 100 yards. It will be basically useless for any range other than the 13 yard point because you have so much angle between the scope and barrel making them converge at such a short distance.

Try setting the gun up so that it is hitting 3-4" low at 20 yards and see where it hits at 100 yards.

[maxicon]

Shimming is also likely to put stress on your scope, which can kink the tube if there's too much. I'd google shimming scope or similar and read up on it first.

You could get a feel for how much it would shift by taking off the top half of the rings and laying the scope in them, then inspecting the rings front and back to see if the scope's got the same clearance.

If it's tilted due to ring or rail height differences, shimming could make it better or worse, depending on which way the offset is.

This would also help you figure out where the problem is. There's got to be something out of whack to make the POI shift as the rings are swapped, and figuring out what is an important first step to fixing it.

The PRW rings are good gear - I have several sets of PRW and QRW rings and have had good luck with them. Still, even Leupold can make a lemon sometimes, and if it's a ring problem, they'll make it right.

Another option would be a one-piece mount, which would get rid of the ring alignment issue and avoid the risk of damaging the tube, but it's yet another expense...

[Pthfndr]

Just get some Burris signature rings with the offset inserts.

[xenophobe]

I'm pretty new to scope's and rings, but the rings are Leupold PRW High Rings, No. 54150. I bought the high rings for my OLL so I could get above the front sight, but I am using this scope on the 22 rimrife for now. The scope is pretty high above the bore site, and for the short distance, 40-feet (my back yard length for bunnies) I guess I might have to shim the rear up to bring the front down... Comments???

Strange. Switching mounts front to rear like that shouldn't have that much inconsistency... the QWR are tensioned, but the rail isn't metal...

I would try some low weaver rings... I know they're crap, but they're generally consistent and I think Ted is onto something.

[maxicon]

Strange. Switching mounts front to rear like that shouldn't have that much inconsistency... the QWR are tensioned, but the rail isn't metal...

Good point - given the quality of Walther's recent .22 offerings, there's a chance the rail's not up to snuff.

Might want to lay a straightedge along it just to see if it's got any warpage.