Scope Shimming Question

[Olympus]

I know this is probably an easy question, but I can't quite seem to wrap my head around the issue to make the corrections I need. I've only ever had to shim one other scope and I had the same issue and I can't remember what I did to fix it.

Situation: I put a 50mm objective scope on a CZ 455 Varmint rifle. I used Leupold high rings, but the bell of the scope hit the top of the barrel before settling into the bottom of the ring. I added two pieces of shim to the bottom of the FRONT ring just to give the bell the additional height it needed to keep from hitting the top of the barrel.

I went to sight the gun in and it was shooting terribly LOW. I have used up all of my elevation adjustment on the scope and I'm still about 2.5" LOW. What do I need to do in order to get some more adjustment out of my scope?

 

[beatledog7]

You raised the front of the scope, and now the gun shoots low.

Think about that. When you raise the front of the scope, you force the muzzle down to bring the crosshairs onto the target. The gun shoots low. You adjust the scope's elevation turret, but it still shoots low, and that's because there just isn't enough adjustment to overcome those shims.

Shim the rear scope ring the same amount as the front. This will bring the barrel of the scope and the barrel of the gun into closer alignment and give you back the adjustment range you need. Then I'd suggest you center the elevation turret and start the sighting in process over.

Shimming both rings will also alleviate the barrel flexing that is undoubtedly also in play.

 

[Coltdriver]

If you assume the rings form about the same circular cylinder and share a common center and you only raised the front ring you are bending the scope! Even a few thousands will put undue stress on the scope. You are not tilting it so much as you are placing the front ring on a plane slightly above the plane of the rear ring! Do that enough and you will dent the scope tube or distort it.

Shim both equally or get extra high rings.

 

[rcmodel]

+1

What he said.

Shimming inside one ring only will warp the tube and possibly cause an internal lens mount failure.

Best get some higher rings, or a smaller scope.

rc

 

[Olympus]

Thanks fellas. I will file this in my memory for future use. I just don't shim enough scopes to remember all these little details. And honestly, I've just about gotten out of rifles except for hunting and have been shooting pistols recently. Forgive the newbie mistake.

 

[bubba15301]

you need extra high rings

 

[Maverick223]

First of all, never shim inside the ring. Shim beneath the base if necessary, if it is a 2-pc. base shim both equally to prevent warping (which can seriously damage your tube and/or lenses depending on the severity of the bend).

In the event that you need to shim for elevation (which would require raising only the rear of the optics) I would recommend that you always use a 1-pc. base/mount with only one exception: Burris Zee Signature rings, as these allow for custom plastic inserts (which are fairly costly, so be sure and budget that in) that will shim the optic as necessary.

 

[Olympus]

The gun is a CZ 455 22LR so the base and ring is all one piece. There's no way to shim other than inside the bottom of the ring. It's a 3/8" dovetail and I could not find an extra high size mount. All I could find was regular high.

 

[WNTFW]

You might find a cure in these sites:
http://www.bkltech.com/
http://www.diproductsinc.com/Products.aspx?CAT=3600

 

[proven]

try using the dip 25 moa base, and a set of pic rings.

i have that base on my 455 and with a 42mm bell am using seekins precision low rings.

 

[Maverick223]

The gun is a CZ 455 22LR so the base and ring is all one piece. There's no way to shim other than inside the bottom of the ring. It's a 3/8" dovetail and I could not find an extra high size mount. All I could find was regular high.

I missed that; are you sure that it's a 3/8in. mount, I thought that they used a 11mm (on all but the 452/455 American)?

If it is 3/8in. these aught to work just fine (these might work, but are a little lower). If it's 11mm they are going to be a lot more difficult to find (the BKLs that WNTFW mentioned above are the only ones that I've found).

 

[Olympus]

I wanted the "clean" and "classic" look of the Leupold rings. I was told that the dovetail was 3/8" so that's the rings I bought. They fit just fine other than they're not tall enough.

 

[Olympus]

I wanted the "clean" and "classic" look of the Leupold rings. I was told that the dovetail was 3/8" so that's the rings I bought. They fit just fine other than they're not tall enough.

 

[Maverick223]

I agree with your assessment regarding the aesthetics, however one can only be so choosy. BTW I looked up the rifle, and according to CZ it is indeed a 11mm mount (which some 3/8in. will fit), so whatever you get make sure that it'll fit the larger dovetail.

 

[nyresq]

I never heard of anyone shimming inside the rings. I would think that would throw off the alignment of the ring to ring level and also the inside dimensions making the ring into an oval.

Get some extra high rings. The rifle you have is not that rare and thhe 50mm by todays standards is not that big. You should be able to fing a properly sized set of rings.

 

[Olympus]

Can't shim anywhere but the inside of the ring on these rimfire bases.

Needless to say, I got the issue fixed and got the scope sighted back in. Had plenty of elevation adjustment this time. Thanks for the assistance to everyone.