Thread: Shimming scope...

I fitted a Nikko Panamax scope to a JW-15.

At 100m it is shooting about 20cm low with scope cranked right up.

I'm a noob at this stuff. I'm assuming that I need to shim the rear mount to provide some lift?

My concern is that if the rear mount is higher than the front, does that not potentially put some strain on the scope tube?

Or is there another way?

You don't need to shim them much to get the change you are looking for.

Shimming the rear ring is OK and will not cause problems. You can cut shims from aluminium drink cans with a pair of scissors. The shim only needs to be at the bottom, about15mm is long enough.

I shimmed the rear mount between titanium action and under the mount base with cut bits of beer can did not take much on my 7 mm WSM and DNZ scope mount as my Swarrrovinsky Z8i did not have enough adjustment.

My rifle is a Browning Mountain Ti I could not get a 20 moa mount anywhere.

It might have been three thicknesses of beer can this then put my rings out of line so I went to the local engineering shop and purchased a section of 30 mm diameter finished bar $5.00 which with lapping compound I trued the bottom half of the rings so there is no bending stress on the scope tube.

If you can do the mathematics you could work out the thickness you need I personally did it trial and error so my scope gave me 3/4 elevation and a full turn on the Svarovvvaskiee target style turret with some to spare so I am never near the maximum travel in the turret adjustment.

At 100 yard zero my scope is 1/4 travel up from maximum down.

All very cheap and works 100%

Originally Posted by xtightg

I trued the bottom half of the rings so there is no bending stress on the scope tube.

Yep, that's the way I'd do it. I check ring alignment and lap as required for every scope I mount, but especially if you're deliberately offsetting the rings. The gear is cheap and the process is quick, well worth it in my opinion. My lapping rod is a piece of 25mm cold-rolled, I stick 600gr wet and dry sandpaper on it with spray adhesive which brings it almost perfectly up to 25.4mm. I've tried lapping compound - the 600gr paper works better in my experience.

These are cheap rings (although look better than the rings it came with) so will try the swapping back to front / turning rings thing and see if that makes a difference.

I have a shim(s?) that came with some Talley rings for my 308, might see if those will work.

Edit: Although any excuse to drink beer. Waikato cans better than DB Export Gold?

Why don't you just get some weaver tip offs for 30 odd dollars

Originally Posted by Russian 22.

Why don't you just get some weaver tip offs for 30 odd dollars

What's the advantage of the tip offs?

Originally Posted by davetapson

What's the advantage of the tip offs?

You shouldn't need any shims or ghetto bubba work

Now's the time to probably ask:

One of the rings has a grub screw set into the base of the ring, that would contact with the dovetail rail.

What's this for? Could I screw it out slightly to get the raise that I'd like? I assume I'd have to thread-lock it to stop it unscrewing itself?

you can buy shim metal from acorn models in chch

https://www.acornmodels.co.nz/

various materials various gauges

Originally Posted by davetapson

I fitted a Nikko Panamax scope to a JW-15.

At 100m it is shooting about 20cm low with scope cranked right up.

I'm a noob at this stuff. I'm assuming that I need to shim the rear mount to provide some lift?

My concern is that if the rear mount is higher than the front, does that not potentially put some strain on the scope tube?

Or is there another way?

The JW 15 factory mounts are a bit...temperamental. I managed to fit a scope to it that on first install had a conflict between zoom ring and bolt handle when the bolt was pulled back - turned one mount round 180deg and scope now barely interacting with bolt. It may be the same if you swap the front and back mounts with each other. And bore sight, as in, bore sight, no fancy laser needed.

Originally Posted by davetapson

I fitted a Nikko Panamax scope to a JW-15.

At 100m it is shooting about 20cm low with scope cranked right up.

I'm a noob at this stuff. I'm assuming that I need to shim the rear mount to provide some lift?

My concern is that if the rear mount is higher than the front, does that not potentially put some strain on the scope tube?

Or is there another way?

A couple of questions... Why 100m? Most will sight in 22LR for 50 or 75 metres. Reason being if you are zero'd at 100m then you are likely to be fairly high in the middle at around 50m. Enough to go right over mr rabbits whole body. I usually zero mine at 25m with subs. This puts them about 1"high at 50m and about zero again at 70m and about 5 to 8 low at 100m depending on the ammo. If you are zero'd at 50m there is a fair ole bit of drop at 100m. More than most would think.

If you do really want it zero'd at 100m , then as Gundoc said, "Shimming the rear ring is OK and will not cause problems. You can cut shims from aluminium drink cans with a pair of scissors. The shim only needs to be at the bottom, about15mm is long enough. "

And the recoil lug screw in the bottom is harmless if left in there. usually it will be screwed down into a hole or groove on air rifles as the spring recoil vibrations on those are savage on scopes. I usually leave them in there. Otherwise they get lost and one day you may need it.....

Originally Posted by timattalon

A couple of questions... Why 100m?

Basically so I can shoot on the NZDA 100yd range.

Being a city dweller, I don't have the option of choosing my target distance unfortunately, and I have no farming buddies within easy reach for an afternoon's plinking.

I want to practice hunting shooting stances and can't do this on the 25m range and don't particularly want to do it all in .308 on the 100yd range.

Maybe what I should do is zero it at the 25yd range and then just set up two targets at 100yd - one to aim at, and one at point of impact. After all, all you are really looking for is grouping size.

Maybe just put a bright point of some kind on the top of the target frame (1" orange sticker?) to aim at and a target at an appropriate distance below that to catch the bullet strike?

Save me bending my scope for no good reason.

Thanks for asking the question.

Originally Posted by davetapson

Basically so I can shoot on the NZDA 100yd range.

Being a city dweller, I don't have the option of choosing my target distance unfortunately, and I have no farming buddies within easy reach for an afternoon's plinking.

I want to practice hunting shooting stances and can't do this on the 25m range and don't particularly want to do it all in .308 on the 100yd range.

Maybe what I should do is zero it at the 25yd range and then just set up two targets at 100yd - one to aim at, and one at point of impact. After all, all you are really looking for is grouping size.

Maybe just put a bright point of some kind on the top of the target frame (1" orange sticker?) to aim at and a target at an appropriate distance below that to catch the bullet strike?

Save me bending my scope for no good reason.

Thanks for asking the question.

Fair enough. If you are looking to practise so when you use your 308 at 100m you will be a better shot, then you can use the 22 at 50 and use smaller targets.

The travel time is determined by velocity and handily enough the 22LR supersonic are usually around 1300-1400fps and centrefire is usually around the 2600-2800fps whch is about double. As a basic rule of thumb, if you want to practise centrefire and use a 22 practise at half the distance. there are other factors that come into play but as a simple start it works.....22LR at 100 does have an issue with groups as it goes transonic before then and the wobble from that can screw groups up. Subs or target ammo is better for that but being subsonic to start with the drop is horrendous at 100m.I also shot 100m at the NZHA with a 22LR but found aiming at much smaller targets and setting up for 50m gave a better result after practising. (Even allowing for the distance.)
@mudgripz could be worth a chat to as he is well versed in the fine art of 22LR.....