20MOA can someone tell me how to shim my scope?

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stang

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I bought a remington 700LA in .308W to target shoot cast bullets. As I don't want to put out a lot of money and purchase a 20MOA mount from Leopold can some one tell me how much to shim the back of my one piece standard Leopold mount, and what the best way to do it is? As it is now there is not enough adjustment in my scope to get me on paper at 100.
 
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Max Owner said:
Are shims bought pre made?

Or buy your own stock and make?
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Poor Man's Guide to Shimming Leupold standard one-piece base:

You need:
tin snips, smooth emory cloth, micrometer, and can of CocaCola.

Step one: drink the coke.
Step two: cut the can apart.

The top and sides of the can provide a couple different thicknesses to play with. .001" is about 1MOA worth of POI change so you can figure out how much metal you need. But that is only a rough estimate - you're going to use trial and error for the most part :) you may have a combination of two or three pieces to get what you need. The fewer peices the better, though.

Cut what is basically square or rectangular washers out of the bits of pop can -- just small enough and the same shape as the scope base to fit underneath and still look tidy. Smooth the edges nicely.

Shim under the back as required to get the elevation you need.

Add shims under the "middle" screw at the front of the base to relieve stress from the base being "flexed" when you tighten it on top of the new shims at the back.

Now take it all apart and clean the heckout of everything before whipping it all back together for keeps with a bit of loc-tite on the screws.

If you have a two-piece base - shimming will make the rings go out of alignment (Shimming lifts the rear one straight up, but not the front one - they're still parallel, but not in line...) and could damage your scope. So even if you don't want to shell out for a 20MOA base - at least get a one-piece base.

I hoep this makes sense - I'm finishing up a night shift here...
 
If you don't want to shell out "big money" on a leupold base, check out EGW basses , they are only about 60 bucks and are a
Mitch better option then shimming basses
 
Shimming is really a stop gap measure and a very poor way to gain elevation. Buy a base, surely there is a used one on EE
 
dizzy said:
Shimming is really a stop gap measure and a very poor way to gain elevation. Buy a base, surely there is a used one on EE
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Leup's standard one piece base doesn't come made with any built in cant like the tactical (picatinny rail) bases do. If you're going to get a one-inch tube to shoot at 1000y with a standard base - you gotta shim it.

My preference is 30mm tubes, and 20MOA bases, as well. But - the standard base has one nice feature -- it has set screws to adjust for windage. Now -- it's another moving part that needs loc-tite after setting it up.... but if you have a one-inch tube, these bases are better at setting up your scope centred for wind to leave you more (and even) adjustments on both sides.

I use a 20MOA picatinny rail base myself, and I like it better than shims, for sure. But it isn't "perfect" for wind - nothing is. With a 30mm tube on top, I have so much lateral travel that it doesn't matter. (I just have to remember that if I ever shoot in hurricane Katrina winds at 1200m, I have 10MOA less wind adjustment on my left side....but like I said, I have something like 30 MOA on one side and 35 or 40 on the other...)

That 10MOA might be enough to put a smaller tube with less adjustment out of the race. I used to run Weaker T models, and if I gave up 10 minutes of right wind to zero it, I thinkit only left 12 or so, I can't really recall) So I think there's some argument to be made for the Leup standard bases...

Spending the coin on a nice base might necessitate spending MORE coin on a new scope. So shimming can buy a bit of time until you can do it ALL the right way.
 
trout bum said:
Leup's standard one piece base doesn't come made with any built in cant like the tactical (picatinny rail) bases do. If you're going to get a one-inch tube to shoot at 1000y with a standard base - you gotta shim it.

My preference is 30mm tubes, and 20MOA bases, as well. But - the standard base has one nice feature -- it has set screws to adjust for windage. Now -- it's another moving part that needs loc-tite after setting it up.... but if you have a one-inch tube, these bases are better at setting up your scope centred for wind to leave you more (and even) adjustments on both sides.

I use a 20MOA picatinny rail base myself, and I like it better than shims, for sure. But it isn't "perfect" for wind - nothing is. With a 30mm tube on top, I have so much lateral travel that it doesn't matter. (I just have to remember that if I ever shoot in hurricane Katrina winds at 1200m, I have 10MOA less wind adjustment on my left side....but like I said, I have something like 30 MOA on one side and 35 or 40 on the other...)

That 10MOA might be enough to put a smaller tube with less adjustment out of the race. I used to run Weaker T models, and if I gave up 10 minutes of right wind to zero it, I thinkit only left 12 or so, I can't really recall) So I think there's some argument to be made for the Leup standard bases...

Spending the coin on a nice base might necessitate spending MORE coin on a new scope. So shimming can buy a bit of time until you can do it ALL the right way.
Click to expand...

Well said trout bum :D
 
If you must shim, ensure you buy rings with inserts, if you don't the rings are no longer true and affect the tube itself. this may be a given to most, but not all and it has hurt more scopes than its helped.
 
Dogleg said:
Shims can cause or correct alignment problems. There's likely something out of whack when he can't get on paper at 100 yards with the cast bullets.
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This is a good point. Usually you can get on at 100y/m..... you just use up so much elevation that you can't get past 700-800y with the thing. Maybe mismatched rings? Bad fit (wrong model) base to action?

And I'm not familiar with cast bullets for rifle. Once this rifle is "on" at 100y -- is it staying there? Like I said - I don't know much about cast bullets - but I can't figure you're likely to get good results at any kind of distance with them. (Or more of us would be on that train....it's gotta be cheaper than Berger and Sierra.)
 
dizzy said:
If you must shim, ensure you buy rings with inserts, if you don't the rings are no longer true and affect the tube itself. this may be a given to most, but not all and it has hurt more scopes than its helped.
Click to expand...

A Leup standard base (if I'm thinking of the right one. I have three or four laying around that have been "surplussed" by rails) is a one piece base and the rings stay true when it is shimmed because the whole base pivots forward when the rear of it is shimmed. The only caution is that a small amount of shim needs to be applied part way up the base as well to prevent "flexing" which does represent a risk to the scope. Not as bad as shimming two-piece bases.
 
stang said:
I bought a remington 700LA in .308W to target shoot cast bullets. As I don't want to put out a lot of money and purchase a 20MOA mount from Leopold can some one tell me how much to shim the back of my one piece standard Leopold mount, and what the best way to do it is? As it is now there is not enough adjustment in my scope to get me on paper at 100.
Click to expand...

Might have found the problem, back to original post.... Is this a Remington LA (LONG Action) in .308? Really? Someone might have built it on an old 30-06 or something - but 308s are SA (Short action) Remingtons....

Do you mean "Left hand"?

If it is a left hand action - odds are you don't have the correct Leup standard base for it. I've been trying to source such a creature for a buddy for almost a year. Nada. Leup doesn't make them now and I don't think they ever did. Keith C at Milcun uses Left-hand actions and he told me he always had to use two-piece bases before he switched over to ambidextrous rail mounts...(Milcun makes a base now - I own a couple and they're awesome. Rem700SA only. I had to use a Badger on my LA 6.5x284)

If you have a Leup standard base and you've screwed it down onto a "Left" handed action - good chance something doesn't fit right. You might need to get something else and start over. (Good opportunity to get the 20 MOA rail everybody's been pressuring you to get)
 
FYI - Leupold LA "Long Range" one pc base - PN 51732 (thats a matt base for the 700 LA) not expensive to do it right.

One thing I always check is the receiver height from front/back. It is common to see the back of the receiver lower than the front. Install the base with just the front screws and check for a gap under the rear. If it's there you need to shim it. (also check with just the rear screw tight and see if the front of the base lifts).
 
Maximize Your available elevation for long range shots by shimming 101.

Step 1 : From your 100 yard scope zero,(or as close to 100 yard zero as you can get.) Find out how many MOA you have untill you bottom out the turret/adjustment by shifting POI down all the way. Not up like you are going to take a 1500 meter shot, but down like you are zeroing for 50 meters is what we need. For this example we have 25 MOA under our 100 yard zero.

Step 2 : Measure the total length of your scope base. The parts where it actually contacts the action, NOT the extension riser area if applicable. We will use 6 inches as our example.

We want to tilt the scope rail foreward so that our 100 yard zero is very close to the bottom of the scopes adjustment range. This way we can adjust our POI up even more, thus extending the range that we can zero the scope for long range shots.

We have 25 MOA available, But we should leave a few MOA available just to be sure we can still zero the scope to 100 yards. So we will work with 20 MOA.

There are 60 MOA in 1 degree. So 20 / 60 = 0.33333 degrees.

Our scope base is 6 inches long. To tilt up the rear, we will have the front still contacting the action, but want to find the dimmension to shim the rear.

SOH, CAH, TOA.

Sine Theta = opposite/hypotenuse. So grab a calculator and punch in 6 inches * Sine 0.333 and you will have the rear shim dimmension of 0.035 inches.

But wait a second. The shims should really be tapered or we will create a bending force in the scope rail.

Most scope rails have two attaching points where the screws pull the mount down onto the action. With some more fancy math we can figure out how much taper should be between the points. This will also help us figure out how to shim a 2 piece scope base.

Find the length dimmesion of 3 locations.

1 Very front doesn't matter because it will be zero or contacting the action
2 Rear of the front base = .75"
3 Front of the rear base = 5.5"
4 Rear of the rear base = 6.0"

Use the same formula : Dimension * sine angle =

Front = 0.000"
back of the front mount point = 0.004"
front of the rear mount point = 0.032"
Back of the rear mount point = 0.035"

Build and taper your shims to these dimmensions and install. Your scope should now zero with 5 MOA left to spare and you should have a ton of MOA left for long range shooting.

Pop can aluminum works great because it will easily conform to the curvature of the action. Of course, this method does not replace the value of a properly tapered CNC scope rail.

I use the NF +40 MOA rail on my .308, and it nearly bottoms out the adjustment of my NXS so that I can now zero all the way out to about 1600 yards.

One last warning, Shimming the back or your rail tilts the scope foreward and moves the objective lens closer to the barrel. Be aware that your butler creek lens caps may not fit if you get too close.
 
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