scope mount shimming?

[dangerranger]

I took my 45 70 to a 200 yd match. it was zeroed to 100yds. thats as far as I can safely shoot in my yard. I thought that Id rezero it easily before the match and be ready. Im shooting a 405 gr boolit at 1400 fps. I needed to raise the sight 21.5". I didnt quite have enough elevation to make it up. So now I need to shim up the scope mount and Im not quite shure how to figure out how much slope Ill need.
Heres my idea,
with the scope zeroed to 100yds, set out two targets one 22" above the other. sand bag the rifle on to the upper target. then without moving the rifle shimm up the rear of the mount till the cross hairs are on the lower target. does that sound like it will work? Thanks all. DR

[EOD3]

Have a look at the information here: http://www.opticsplanet.net/secure-scope-mounting-system.html

If you still need help, let me know.

[NickSS]

I have shimmed quite a few scope mounts for various reasoned and to get them on at longer ranges is one of them. I do not know what type of scope or mount you are using so if you have front and rear bases generally I cut some aluminum pop cans and make strips the length and width of the mount and cut or drill them for the screws that hold the mount. I usuall make three or four of them. I then go to the range and install one or two of them under the rear mount and see if that fixes the problem if not I add more shims until I get the elevation that I want. I have added up to five shims on some 22 RF scopes to get on at 200 yards.

[dangerranger]

Nick, its a weaver one piece mount. the problem is I dont have a 200 yard range to test from. I was just wondering if I could put the 22" of drop in and be on paper for the next match or if Ill need to shoot it at 200yds to know for shure. DR

[45r]

burris signature rings with +20 and -20 inserts will work sometimes and not put stress on your scope tube,if you shim you might want to get a lap kit to keep from binding up your scope.

[Kskybroom]

Somethings Not Right??
Got right scope
Scope Bent
Screws Tight (to rifle, mount, right screws)
Zero Scope ( turn Scope all the way to the left count click all the way to the right 1/2 will be center then up + down )
Mounts (right mounts, bent, filed,sanded, mounted right, front hieght same as back)
Top of Rifle ( Been Filed,sanded, machined,)
????

[dangerranger]

Somethings Not Right??
Got right scope
Scope Bent
Screws Tight (to rifle, mount, right screws)
Zero Scope ( turn Scope all the way to the left count click all the way to the right 1/2 will be center then up + down )
Mounts (right mounts, bent, filed,sanded, mounted right, front hieght same as back)
Top of Rifle ( Been Filed,sanded, machined,)
????

Scope just doesnt have enough elevation adjustment for the 45 70 at BP speeds. 405 gr bullit at 1350fps drops 24" at 200yds. thats why they comonly use tall tang sights for irons. what Im really getting at is, Im looking for a way to figure out how much to shim the mount without alot of back and forth to a public range, on a try and see basis. shimming the one piece base should not put a strain on the scope, just put a slope on the mount. DR

[NickSS]

With a one pice Weaver mount you can shim the scope under the rear of the scope mount or inside the botton of the rear ring. I usually shim the ring first by cutting a piece of cardbord from a box of 22 LR and slipping it under the scope. You can test the results at 100 yards easily. All you need to do is get a 100 yard zero then increase elevation until the bullet hits 15 inches high. You will then be on at 200 yards with black powder loads. I just did this on a scope I mounted on my Sharps rifle and it worked fine.

[mattbowen]

Dangerranger;

I have done that same thing that Nickss is saying but on alot of modern case rifles but I use a thin piece of tin (cut from a coke can) put just under the scope in the rear ring then re-sight at 100yds. in the back yard. For my 30-06 and 308 200yrds. is about 4" high at 100 so if your 200 mark is at 15" high at 100 then mark your target with a 100 yard zero and then go up 15" four 200 and see if you have enough adjustment.

Matt

[bigted]

first i ever ran into this is with my newest marlin lever. it came with shims to do just this very thing. the instructions say to either put them under the rear or front wich ever the case is called for and tighten the mounting screws down and try it. luckilly mine didnt need shimming but i now have a small pack of shims that came with my rifle.

i like the idea of using the aluminum pop can as shim stock as ive used these as shims to shim a harly motor in the frame to lessen the vibratino as the cases if bound will couse a vibration in them more then usual.

shim n shoot...shim n shoot...shim n shoot. then you will know for sure.

[oneokie]

From Leupold: .001" under the rear mount equals 1" at 100 yards. Check the length of the rear mount screws to make sure that after shimming, you have enough thread engagement to secure the mount. You may have to use longer screws than came with the mount.

[excess650]

Burris Signature rings with the changeable inserts IS the way to go. They do not stress your scope tube. For 1" scopes, inserts vary from "0", +/- .005", +/- .010", and +/- .020". With -.020" in the front and +.020" in the rear, you will have effectively tilted the scope .040" in relationship with the base, but without stressing the tube.

[dangerranger]

thanks guys! I have a brass shim kit with the shims just wider than the mount. with the curve of the reciver they should be just right. Ill give it a try. DR

[Larry Gibson]

dangerranger

Suggest you adjust elevation (of the scope or the base whichever is adjustable) so it is 2 moa up from bottom. That will leave enough adjustement for load variation at 100 yards. Then shim the rear of the scope base until you are again zeroed at 100 yards. That will then give you the maximum amount of elevation possible with your scope/mount. It should then have more than enough to make for a 200 yard zero if not a lot farther.

Larry Gibson

[Reverend Recoil]

You should set the scope's reticle to mechanical zero before determining the amount of base shimming needed. That way you will have maximum elevation available for any range you choose to shoot. Hold a hand mirror directly to the objective lens and look through the scope. If you see two sets of reticles adjust the elevation until they merge. You may have to shine a light on the mirror to see it well. If you have Redfield-type adjustable mounts you can do the same to the windage and re-bore sight the scope in its mount. With a little time and patience you can get your rifle shooting in the black of a 100 yd bullseye without adjusting the scope’s internal settings. Once that is done, turn the scopes adjustments to the center of the target. Good luck.

[rockrat]

Your scope doesn't have 12" of elevation @100 yds available? Equals 24"@200. It should have that much available, I would think.

If you could get .010" thick brass shim stock, that might be enough to go under the scope base.