shim a scope base ?

[Frankr]

If you were going to shim a scope base to add elevation to you scope..how many Thousands would you add per moa ?
You would say shim under the back of the scope base to add elevation right ?
I know you can buy shims...If you can not get a base or have one you have machined you can add a few shims under the rear of the base to gain MOA elevation right ?

 

[SBS]

Shim material will add approx. 1 MOA per .001" thickness and under the rear base to add elevation. Not the ideal way to add elevation adjustment, but has been used many times.

 

[1885Winman4590]

I cut a 3/4" long piece of a feeler guage that is the correct thickness that I want use. Then heat it up to take temper out. Then drill holes to match scope base holes and bolt it down. It has worked well for me and my applications

 

[M-61]

Marlin supplies two shims for their 1895 model. It has a long picatinny rail factory mounted. Interestingly the shims are some sort of what I will call 'plastic like material. Almost like a fiber and plastic composite. They work.

 

[Ggmac]

If you have 2 piece bases don't shim ! One piece is ok . Remember with 2 piece bases , shimming just one would bend , torque your scope .
Both bases need to be on the same plane

 

[Frankr]

If you have 2 piece bases don't shim ! One piece is ok . Remember with 2 piece bases , shimming just one would bend , torque your scope .
Both bases need to be on the same plane

I have a 20MOA TWO piece NF base on one of my 700's so I don't think a .020 shim under a rear base would be a problem. Would it ?

Thanks for the info guys...I have a scope that may work well but it only has like 20 MOA up n down...So using a windage adjustable ring with a 20 MOA slant will help it be useful to 1K. I think..

 

[JohnKielly]

I have a scope that may work well but it only has like 20 MOA up n down...So using a windage adjustable ring with a 20 MOA slant will help it be useful to 1K. I think..

Likely it will be OK at 1000 yards, but useless at short distances.

What you need is a scope with more adjustment & then, for ultimate refinement, 20 MOA built into you mounts.

The average non-magnum calibre will need 25 MOA adjustment +- from 300 yards to 1000 yards. If you seriously expect to be able to crank accurate wind on at the longest distance, then you need the centre of adjustment of the scope to be reasonably close to that elevation - let's say within 10 MOA. Therefore you'll need 15 MOA adjustment available to you to get to 300 yards (25-10), a tad more to 100, and again at that distance, you shouldn't be close to the downward elevation stops - let's say a comfortable 15 MOA away.

Doing the maths, you want 15 + 15 moa adjustment below centre to get to 100 yards, in other words with at least 60 MOA total elevation available if you want to be able to crank your sights accurately over 100-1000 yards range & that's in addition to a 20 MOA rail or mount set.

 

[284winner]

If you have 2 piece bases don't shim ! One piece is ok . Remember with 2 piece bases , shimming just one would bend , torque your scope .
Both bases need to be on the same plane

Why do they make two piece 20 moa bases where the rear is higher than the front ? Just curious. I've only used one piece moa bases so please educate me on that.

 

[Ggmac]

When made they are both cut on the same plane . It would be no dif than cutting a 20 moa base in part .

 

[Ggmac]

Fjim don't shim any 2 piece base . A factory 2 piece base is made in 20 moa is going to be the same issue if you shim only the rear base , you will stress or damage the scope !
All this is only pertaining to traditional ( no insert ) rings .

 

[hottshott526]

Formula:
<> Offset in .xxx's / Ring Spacing X 3600 = Inches of Offset at 100yds
<> Inches / 1.047 = MOA Offset at 100yds

Say with .030's at 5" of spacing = 21.6" at 100yds (20.6-MOA @ 100yds)

But I wouldn't shim a 2 piece base set for fear of bending the scope tube. IMO

I've shimmed many 1 pc bases and then bedded the base to the action to take up the air gap in between. The gap is not much but it does make a difference.

 

[Turbulent Turtle]

Formula:
<> Offset in .xxx's / Ring Spacing X 3600 = Inches of Offset at 100yds
<> Inches / 1.047 = MOA Offset at 100yds

Say with .030's at 5" of spacing = 21.6" at 100yds (20.6-MOA @ 100yds)

But I wouldn't shim a 2 piece base set for fear of bending the scope tube. IMO

I've shimmed many 1 pc bases and then bedded the base to the action to take up the air gap in between. The gap is not much but it does make a difference.

Thank God you introduced some sense into this thread. I could not believe what I was reading up to now, so I hope it was just due to a misunderstanding on my part.

Anyway, hotshott256 is correct in introducing the length of the spacing between the middle of the rings; that is exactly what predicates the mount of added incline in the setup.

For a one piece ramp, you also need to factor in the length of the ramp that you will be shimming; adding .001 inch to a 3 inch ramp will produce more MOAs of inclination that adding a .001 inch to a 6 or 8 inch ramp. The answer is in the arctangent of the base length.

If you have a two piece mount, I would suggest STRONGLY that you look into the excellent Burris Signature Zee rings as the ONLY safe and predictable method on introducing an offset to your scope short of a dedicated 20 or 30 MOA one piece ramp. And even with the Burris rings, the distance between the middle of the two rings is crucial in determining the resulting offset using the various inserts.

ETA: Corrected the name of the manufacturer of the Zee rings. I blame society for my earlier error. That and jet lag.

 

[savagedasher]

I cut a soda can with shears works for me .
Larry

 

[Frankr]

OK thanks I am going to use the burris sig insert rings...windage adj Rings...I have had that set up on a hunting rifle for twenty years and it has never moved...So I will use the insert rings to gain 20MOA elevation and the windage to keep from turning the scope..My rifles several ... Dead on at 200 yards...09 to 1 1/4 high at 100 yards...never need more than 22 to 23 mins to get to 1,000 yards...and I very seldom shoot that far but 4 to 6 is common and had a few this year close to 950 yards.. I just want to try and make this scope that has 40 MOA elevation and 40 moa windage useable on this one rifle I have...I think I can get the windage no problem then if I can get the 20 MOA elevation then it can work and work well...

Thanks for the info..