Geometric puzzlement

[Baldie]

In an ideal world ....


This method is for AIR rifles only. Most of this hard work isn't necessay for CF.

Step.1

To get the very best from scope, you should centre it. This means centering crosshairs to the boreline of the scope.

To get the ret centred, you mount the scope on some wooden (or other soft surface material) V's. the idea is that you can rotate the scope along its axis, without the turrets touching/fouling on anything.

Once you have this situation, you rotate the scope right then left by 90 degrees, adjusting the turrest as you need to. The idea is to get the crosshair (dot or whatever is at the centre) to stay in the same position as you rotate the scope. Once the ret is ACTUALLY adjusted to the centre of the scope, you'll find that when the scope is rotated, the crosshair/dot will stay in the middle position. [The scope will rotate around the 'centred' crosshair.]

Step.2

Mount your scope. Use your usual method to get the vertical line true to vertical over the boreline of the barrel.

Arrange your rifle to shoot at a 25 yard target. If possible the rifle should be held in a gun vice. It helps to work out what actually is going, rather than what you might think is going on, but maybe isn't.

Impliment all usual safety procedures, before firing a single pellet at your target.

In an ideal world, your pellet will have landed within an inch of where you expected the pellet to land. I doubt this will have happened though.


Mindful I'm talking "ideal world" here, the difference between where your scope is pointing on the target, and where the pellet lands, is the combined error value of the scope mounts, and the mounting point to the bore line of the rifle.

Step.3

What you do next (typically) is to recover the error in the mount/rail/bore, by adjusting the turrets [which means pushing the reticule to one side of the scope body] to remove this error. The more you push the reticle to one side of the scope tube, the less your chance of enjoying the full adjustment the scope normally offers for holdover, and windage. It's almost like a handicap value.

If you have to use half the scopes elevation adjustment removing the mount/rail/bore error, it may seem like your scope isn't performing the way it should. In the situation highlighted above, it's the rifle [mount/rail/bore] that prevents your scope working as well as it could.

So getting back to 'ideal' worlds, you shouldn't use the turrets to get a zero, you ought to use adjustable mounts to get the scope zeroed. Once/if the scope is zeroed this way, the turrets will provide the full range of adjustment they were designed to.


Not practical to do this?

Expect a compromise with your scope then.


We had no end of problems reported from shooters trying to mount long scopes on rifles that were plainly never meant to have then fitted. There is at least one model that even the manufacturer recommends the use of a single mount, to keep the action lined up.

Once a long scope was mounted to this rifle, it was practically impossible to get the rifle zeroed and enjoy the full mag and turret range offered by the scope. Evidence of this, is a dark crescent in the sight image at low mag. We took back a number of scopes that worked perfectly, but had been put on rifles with alignment [mount/rail/bore] problems.


The moral of the lesson? Don't try to use high mag scopes without using adjustable mounts. People will (as they are fairly expensive at £50), but don't be surprised if your setup won't, no can't work as well as your old lower mag system.

Just a word to the wise.

[Barry]

Thanks Baldie, a very informative and helpful response. Being new to this I sat scratching my head for hours, then someone at the club said 'put some packing under the rear scope mount', which I guess, for what I do and what I do it with, is good enough.

But, the method doesnt appeal to my sense of the way things 'should be' or your 'ideal world' scenario.

I should imagine, that packing the rear scope mount will misalign the fit of the tube through the front mount by tilting the scope by a tad, and that doent fit with my ideal either.

Are adjustable scope mounts available for a HW100 with a scope with 30mm tube?

Again, Many thanks

Barry

[sarf]

But, the method doesnt appeal to my sense of the way things 'should be' or your 'ideal world' scenario.

I should imagine, that packing the rear scope mount will misalign the fit of the tube through the front mount by tilting the scope by a tad, and that doent fit with my ideal either.

I fully support you Barry, stick to your principles and do it right! If you want to be even more fussy, insist on one piece mounts, and lap the tube to the mounts to avoid any misaligment strain on the tube.

Tedious but satisfying.

P.S. on a lot of (especially German) scopes from years back there was only elevation adjustment, no windage adjustment; the elevation turret had no cover as you were expected to adjust it in the field rather than doing "hold over/hold under". There was no windage turret because you were expected to have adjusted/aligned the mounts in the first place.

[sarf]

Are adjustable scope mounts available for a HW100 with a scope with 30mm tube?

http://www.sportsmatch-uk.com/atp61.htm -

ATP61 - New Adjustable Elevation and Extra High Two piece 30mm Mount. Saves having to pack the rear mount. Point of impact can be adjusted on the mount. The height is between 1.5 and 2.8mm higher than our standard 30mm high range.
Please note both front and rear mounts tilt to maintain correct alignment.
Air Rifle / .22 Rimfire Rifle 30 mm High range for 9.5 mm - 11.5 mm dovetails up to 60 mm Lens Dia.

(I have the one inch Sportsmatch adjustable which is one piece).

[Barry]

Sarf......What is 'lap the tube to the mounts'?

[sarf]

- using very fine abrasive to ensure that the inside of the mounts are perfectly round and exactly the same diameter as the tube (they certainly won't be on mounts that cost £30 - £50).

You can using fine grinding paste on a length of 30mm steel bar (ideally), or you can stick a bit of e.g. 1000 grit wet-and-dry to your scope and rotate that in the mounts (see http://www.bloom.co.uk/images/sportsmatch_honing-s.jpg)

Warning (1): the latter method will inevitably tend to over-bore the mounts due to the thickness of the paper, so proceed with great caution. The "lapping bar" method is superior - if you can find a piece of perfectly round 30mm bar . . .

Warning (2): doing any of this is regarded as eccentric/daft by most airgun owners