i want to shim a rear warne base to give myself some extra elevation. how thick a shim do i need?

I have always worked on the concept that a 1/100th change at the scope = 1+/-" change at 100 yards.

Jeff

Anybody here take sophomore geometry in high school. For you Brits...What???

This is a simple problem in similar triangles and ratios.

shim size/Length of base = target raise of impact/range to target.

Units must all be the same for calculations. eg if you select feet, set all dimensions in feet.

KS,

cut some strips from a soda can and go from there.

Rich
DRSS

K, I'm going to assume that you are wanting to do this for a Steyr Safe-Bolt since you own so many of them.

Have you checked with CDNN to see if they have any of the 20 MOA Picatinny rails left? I bought one for my HB 308 and it was a bargain.

You have to be very carefull how and how much to shim a base for elevation. If you aren't very careful you can torque your scope tube and ruin a scope. A base with built in elevation is a much better way to go.

IIRC you could use a 2pc elevation base for an Browning A-bolt I'm pretty sure they have the same hole spacing - you could call Brownells Tech to make sure...............................DJ

quote:

Originally posted by DMCI*:
Anybody here take sophmore geometry in high school. For you Brits...What???

This is a simple problem in similar trianges and ratios.

shim size/Length of base = target raise of impact/range to target.

Units must all be the same for calculations. eg if you select feet, set all dimensions in feet.

I can tell you are good at math, by your spelling
I was also the top student in honors geometry without doing the homework, and your misspellings are invisible to me, but not my spell checker.
I have also noticed that most people think that 3% alcohol in beer is an ingredient and not a ratio.

What does it all mean?
Sometimes we have to do the problem more explicitly for them.

If your rear base is 6" from your front base and you want to raise you point of impact 20" at 100 yards = ~20 moa, then here is how it is figured:

Distance between bases/ distance to target = change in base height / change in point of impact

6"/100 yards = shim/ 20"

6" / 3600" = shim / 20"

shim = [20"] [6"] / [3600"] = .033"


If your bases were 4" apart, and you wanted to raise the point of impact 5" at 50 yards, then


4"/50 yards = shim/ 5"

4" / 1800" = shim / 5"

shim = [5"] [4"] / [1800"] = .011"



This is how the book "Mathematics for Electricians and Radiomen" by Cooke was written during WWII. The same problem is re-worked as an example with different constants to allow a reader with many missing assumptions to infer the process.

quote:

Originally posted by djpaintles:
K, I'm going to assume that you are wanting to do this for a Steyr Safe-Bolt since you own so many of them.

Have you checked with CDNN to see if they have any of the 20 MOA Picatinny rails left? I bought one for my HB 308 and it was a bargain.

i have those on a couple of heavys. this is a light weight sbs tactical 20 inch and i wanted to keep the weight down. that full length 20mao steel base is a bear.

quote:

Originally posted by KSTEPHENS:

i have those on a couple of heavys. this is a light weight sbs tactical 20 inch and i wanted to keep the weight down. that full length 20mao steel base is a bear.

What cutting the 1pc base into 2pc's and getting rid of the excess steel you don't need? It would still have the taper and be parallel so as not to torque your scope.......................DJ

Unless shimming one end of a one-piece base, be sure to re-lap the rings after shimming the base to avoid potential damage to the scope from mis-aligned rings.

Otherwise, I would use Burris Signature Zee rings with offset (pos-align) inserts. No lapping, variable offset in any direction, works great.

Andy

quote:

Originally posted by tnekkcc:
My long winded boring tirade about how I would never lapp rings, but glass bed the mounts to the receiver with an alignment fixture....with or without shims

Wow, you're able to maintain the same base spacing from front to rear across 100 different rifles? Short, long actions, different makes, etc.?

Andy

Not the same base spacing.
The same alignment of mounts parallel to the bore.

Or the same co planer alignment between the two mounts, them both together having the 20moa incline with respect to the bore.

All Weaver rings are then left un modified and can go from rifle to rifle without introducing a bind.


Here is the seat of the pants tolerance stack up:
1) Bore....nice and straight
2) Bore to receiver....co axial and rigid
3) Receiver to mount.....poor fit, has gaps, flexes, and twists. 5 of 6 degrees of freedom are problematic.
4) weaver Ring manufacturing tolerance... very accurate alignment of Weaver dovetail to ring bore
5) Scope body tube...very round and straight


Everything goes to hell in 3).
It is the mount to receiver fit.
I put epoxy between them and then clamp them with a fixture that forces them into alignment.

When the epoxy hardens, I take the fixture off, and any rings put on that rifle seem to have already been lapped.


I would like to say I invented this, but lots of people invent this process out of necessity.
This is how Boeing aligns fixtures.
They do not lap holes for alignment.

I don't think that you could really accomplish anything by lapping Weaver rings. But I'm convinced that lapping Leupold, Redfield, Ruger, and Warne rings gets you a better fit between the bearing surfaces of the rings and the scope. Without a set of alignment rods, it would be difficult for most people to really "see" that their rings weren't aligned properly, despite having a well calibrated set of eyes. Alignment rods don't lie, but they can be darned annoying if they don't align properly and you're in a hurry to get the scope mounted, zeroed, and into the field!

Jeff

No shims.

Burris signiture zee rings with offset inserts if necessary......not too heavy and works well.

woods

quote:

Originally posted by Buliwyf:
No shims.

We put shims in a lathe, shims in a car, shims in a jet engine, but no shims under a scope mount?

The pressure under a mount is so low that the shim can be made of paper.
The environment under a mount is so benign, paper would last longer than you.

But I don't use shims in long term compression on a Mauser scope mount because the mount fits the receiver so poorly. The shim can conform to the mount or the receiver, but not both.
I use tiny shims that only fill of small part of the joint area to keep the mount aligned until the epoxy hardens.
Then the little shims are embedded in epoxy, and the majority epoxy area with no shim can take the wimpy compressive force of two 6-48 screws.

quote:

Originally posted by tnekkcc:
Not the same base spacing.
The same alignment of mounts parallel to the bore.

Or the same co planer alignment between the two mounts, them both together having the 20moa incline with respect to the bore.

All Weaver rings are then left un modified and can go from rifle to rifle without introducing a bind.

Ah, OK. I misunderstood this part of your explanation in the other post:

quote:

Any scope can move from any rifle to any rifle and take the rings with it.

Thanks,

Andy

quote:

Originally posted by 260remguy:
... Without a set of alignment rods, it would be difficult for most people to really "see" that their rings weren't aligned properly, despite having a well calibrated set of eyes. Alignment rods don't lie, but they can be darned annoying if they don't align properly and you're in a hurry to get the scope mounted, zeroed, and into the field!

Jeff

I assume you are speaking of the two-piece, pointed rods? If so, it is important to try them in multiple spots along the axis of the scope tube. Otherwise, a single alignment only verifies that the two rings' axes intersect, but not that they coincide. By trying in multiple places along the axis, you are verifying that the axes in fact coincide if you have to make no further adjustments as you move it.

I still prefer the Burris Signature rings (with offset pos-align inserts if necessary). They automatically align to the scope tube itself, and any imperfections it may have, guaranteeing no bending stress.

Andy

I recommend the Burris Signature rings and the Burris Offset Ring Insert Kit for your application. Basically, the Burris system allows you to raise and then lower the rear and front rings equally to aviod bending the scope tube and cracking the glass.

Ask scope manufactures what they think about shimming.