Scope Shimming

CS8161

I have a question about scope shimming. I have a scope mounted on a rifle and I was at the range today sighting it in. I have the elevation adjustment cranked all the way down and the rifle still shoots high. Where do I shim to lower the group? I can't shim under the mounts so I will have to shim inside the scope rings.
I appreciate any help anyone could provide.
Thanks in advance!
Chris

Chris8161
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Mobuck

Sure you can shim under the bases. Aluminum cans work pretty good. Cut out a piece the size of the base and make the holes to match. To lower the impact, shim the front base.

Mobuck

CS8161

Its a military mount on a British Enfield 303 rifle. I can't get under their to shim. So, if I want to lower the group, I should shim under the front ring? Put a small piece of shim stock under the scope before I sit it in the ring?
Thanks

Chris8161
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Tailgunner1954

To raise the group you shim under the REAR of the scope (tilt the front of the scope down).
The amount of shim for a 3" ring spacing is about .001 shim per Inch @ 100 yd (.010 shim will move the group about 10" at 100 yd)

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Some guys like a mag full of lead, I still prefer one round to the head.

coyote-man

Mobuck is right - shim under the front base. Not really a very good idea to go with shim under scope its self.
Brownells sells shim packs for under the bases, very handy to have.

grizzclaw

If you have it "cranked" all the way down, isn't it going to hit high?

Thanks, Grizztribefans@sssnet.com

CS8161

I have to lower the group. The rifle is still printing about 8" high and I have run out of downward elevation adjustment on the scope. SO that means that I have to shim the front of the scope up, correct?
Thanks all for the input,
C

Chris8161
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Tailgunner1954

Correct Chris
Use a shim in the .010-.012 range under the front of the scope. A cheap set of feeler gauges (from the auto parts store) is a handy source of shimming material for this type of job, or you might get lucky and find a "assorted" package of brass shim stock material.

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Some guys like a mag full of lead, I still prefer one round to the head.

LSandBinc

Chris, Try to cut your shim to fill the whole ring half so as not to chrush the scope tube. What I normally do is center the crosshairs by counting the turns of the adjusters the experiment with different shim thinkness til I get thecrosshairs close to center on my bore sighter.
Good luck,
Alan

CS8161

Thanks for the help everyone! Now I know which direction I want to take to get this thing shooting right!

Chris8161
Admit nothing, deny everything, demand proof!

spclark

You'll be doing yourself and your scope a large disservice if you shim it now, with the elevation screw run out to the max. No scope will work well at the extremes of the adjustments possible.

To accurately "re-zero" the crosshairs, you can use the "average" method to get close (turn the adjustments lock to lock while counting the turns, then come back to center by coming back 1/2 the turns from one extreme). Some folks stop with this, but you'll do even better if you take a small cardboard box that's wide enough to act as a substitute for your rings. Cut a V-notch in opposite sides of the box sides so you can lay your scope in the notches, then tape or otherwise secure the box to a firm support. Rest the scope in the nothes & rotate while sighting thru it & you'll quickly see how far off "center" your crosshairs are! Make small adjustments in L-R and U-D & rotate again (usually only one screw at a time!), until you're satisfied with the centering. Now remount your scope & begin with a rough bore-sight adjustment & shim as needed until you're close enough to use the adjustments themselves for fine-tuning.