Shimming a 'scope

[spud]

i added a 27 thous brass shim to my nxs and gained exactly 20 moa dave

[spud]

[ovenpaa]

Nice neat job Spud, that does tie in with my initial calculation of 14thou for 10MOA for the distance between my scope rings. Does the shim have a taper it?

[spud]

nope Dave 27 thou all over

[Dougan]

Arrr, so that's a 'shim'.

[dazeroo]

With reference to the thickness required, surely it would vary depending on the distance between front and rear ring?

Someone who was brilliant at trig at school could probably work it out. Personally I could never grasp trigonometry. A black art, surrounded in mystique!

Daz.

[Meaty]

Hello,
I have just had to shim the rings in my wifes 223 as it was running out of elevation somewhere between 400 and 600 yards! I was lucky enough to have some 4mm wide self adhesive shim tape in 3 thou and 5 thou left over from a tooling job at work. I built up layers on the back edge of the rear ring (in the scope channel), left a gap, and then built up a few less layers in the front edge of the rear ring. Moving onto the front ring I placed two layers of the shim at the rear end and checked for fit with the scope. I then masked up the scope well with release compound and put a generous dollop of 2 pak bedding compound in the lower section of the rings and installed the scope as normal. The bedding compound migrated into the voids between the shim tape (and around it) and made for a very stable platform with 100% contact with the scope-just got to remember to clean off any over spill before it fully sets and use lots of release agent! Very happy with the results as it certainly looks good. As for shooting results-havent got a clue but I will find out tomorrow at Thetford Gallery.

[DL.]

i added a 27 thous brass shim to my nxs and gained exactly 20 moa dave

After a lot of considering my options (mounts are a nightmare ) I had to do the same a couple of months ago - front and back, between bases and rings, in order to give clearance for a long weaver rail.

It's worked & I now have the elevation I need to get a normal zero.

[Dougan]

With reference to the thickness required, surely it would vary depending on the distance between front and rear ring?

Someone who was brilliant at trig at school could probably work it out. Personally I could never grasp trigonometry. A black art, surrounded in mystique!

Daz.

That's a very good point Daz.

When I measured the rear sight on my TR it gives 10MOA for 0.1" on the scale. Interestingly it is the same measurement on the front sight scale - but both are based on the eye being only a few inches away from the rear sight. So, the futher away from your eye, is whatever you are elevating (scope or iron), the more you will have to raise it to gain the same elevation of the angle of the barrel....

If you practice the black art of trigonometry - to be spot on you would need to account for both the distance the cross hairs are away from the front lens of the scope, and the eye relief...

Edit - also, I'm not sure that 'shimming' the front and back mounts differently would help - it would be better to raise them equally (keeping it level), as it is the raising of thecross hairs within the scope that matters (although I could be wrong on that point :? :lol: )

[ovenpaa]

Edit - also, I'm not sure that 'shimming' the front and back mounts differently would help - it would be better to raise them equally (keeping it level), as it is the raising of thecross hairs within the scope that matters (although I could be wrong on that point :? :lol: )

What the shimming is doing is making the barrel point up slightly relative to the 'scope on an assumed horizontal plane. I went back and did the math again for my scope based on the distance between the rings and came up with .014" for 10MOA. What I should do is machine a taper of .028" on a suitable piece of material over the distance the rings cover then cut two sections out to sit under the pads so the rings are always at the right angle and do not unduly stress the 'scope tube.

Notice I said 'what I should do....'