Shim rings or bases?

[MD]

I tried scoping a Marlin 336 but even with the scope adjusted all the way to the bottom, the rifle still shoots 3 feet high at 100 yards.

Should I raise the rear base with a shim to lower the front end of the scope, or put a shim in the bottom of the rear rings? Or both?

Or is that even the right approach?

 

[maynard]

Shim the base. If you shim the the bottom of the rings you are reducing the diameter of the rings and can bend or dent the scope tube. By the sounds of it you should start off with about .060" under the rear of the base.
One thing you did not mention is what type of bases and rings you are using. Is there a chance you have them on in reverse? Not trying to be smart ass here but sometimes the simple things are the problem.

 

[MD]

Thank you maynard,

They are Weaver bases for the Marlin and Weaver rings and scope that came directly off another rifle of mine that shot to point of aim no problem.

I didn't notice that the bases were different from each other.

What should I make shim out of? And do you mean I should only shim the rear of the base? Not the whole rear base?

 

[maynard]

Ok so you have a 2 piece base. Take the rear base off ( you will have to anyway) and just compare the height to the front base. If it is shorter in height switch them front to back.
Now if you need to shim the rear base you want to cut the shim about the same size or slightly smaller that the base, this way it is solid.
For shims you can use an aluminum pop can the material is about .005" You can cut a strip of it the width you need and fold it into the length you need. A sharp pair of scissors will work to cut it. Poke some holes for the screw to go through and you will be good to go.

 

[manitou210]

I would think you must lower the rear base, you will only go higher if you shim it up

 

[Ganderite]

manitou is right. It is the front that has to be raised.

The bullet will move about 1" for each thou. You should shim 15 to 20 thou.

if it was my rifle I would first check to see that the bases and rings are all identical heights. if they are, I would scrap the two piece bases and buy a one piece base and try that. A base is cheap.

If rifle still shoots hi, I would then shim under the front of the base. The advantage of the one piece base is that both rings will tilt in perfect alignment. This reduces stress on the scope.

I use brass shim stock that comes in 5, 10, 15 and 20 though thicknesses. Most long range scopes get a 20 thou shim under the rear base.