Target Sports

SCOPE MOUNTING GUIDE PART THREE: ALL SCOPED UP

Created on 14th May 2009

MARK CAMOCCIO provides some troubleshooting tips in the final part of setting up the scope

IN THE previous articles, I`ve dealt with the general procedures for setting up a scope correctly within the mounts, then zeroing the rifle. In this final piece, I'll touch upon some problems which can hamper the proceedings and cause much scratching of the head.

My usual approach to zeroing an air rifle has been fairly casual, yet it has served me well over the years. Set the rifle in the mounts, adjust the turrets until the pellet falls behind the crosshair - job done. Except that it's not - that's just the start!

Certain schools of thought exist as to best practice, and in an ideal world the scope should still be ‘centred' before and after it is zeroed. While this can be ignored much of the time it can be necessary to follow the rules, especially if problems arise.

The term ‘centred' concerns having the turrets set to the very mid-point of their adjustment range. This is achieved by firstly winding each turret right round to one end of their spindle mechanism, then winding the turrets all the way through until they come to a stop at the other end of the adjustment, making a note of how many revolutions it takes to complete the motion. The turrets then need to be wound to the mid-point. For example, if eight revolutions of the turret are noted, wind the turret back four revolutions. It will now be exactly centred.

Why do we bother to centre the scope at all? Because by completing this procedure, the optics/lens mechanism is put under minimal stress. In the worst case scenario, in order to achieve zero the turrets need to be wound very near to the end of their adjustment. In this situation, the internal locking rings and seals containing the lenses and suchlike within the scope can be physically compressed, even crushed, and with adjustment set at the extreme end of its range, a less than perfect optical set-up exists possibly causing further irregularities and aberrations along the way.

To be perfectly honest, I've never been too concerned regarding this procedure. I find that most scopes fall into line, and it's really not worth worrying about unless problems arise. You'll probably know when the turrets are nearing one end of their adjustment range, as turning the turrets becomes progressively stiff and awkward. However, if adjustment is nice and smooth and the scope can be zeroed, then all may be well. Before a smug grin is permitted, though, a basic cross-over check needs to be carried out, which I'll cover later.

In the worrying event that one or both scope turrets run out of adjustment (making zeroing the scope impossible) then several options exist to remedy the situation. Firstly, fixed compensating mounts can be used. These can be supplied as twin rings or in a one-piece variety. Both designs will have a built-in progressive angle, bringing the sightline closer to the bore and effectively freeing up much more adjustment in the scope. The mounts can be simply reversed to achieve the opposite effect, depending on whether a decrease or increase in elevation is required.

A cruder, cheaper, yet potentially more risky option is to simply pack the appropriate mount by placing a thin layer of plastic or film negative inside the scope ring, underneath the scope. If this route has to be taken, then the best option is to make a pleated aluminium foil insert, as shown in the photograph. This cleverly builds a much snugger, truer fit for the scope, helping to minimise any warp imparted to the body tube. I've pinched the idea from Nick Jenkinson and, having used it in a few emergencies, I can confirm that it works well - believe me.

The final option of a totally adjustable mount should sort the problem and allow for the holy grail of a centred scope to be dropped into place too. Sportsmatch produces top-quality British-made scope mounts, which are fully adjustable, in both twin ring and one-piece designs. Both options have a two-part body which fits together via adjustable bolts. The pre-centred scope is simply locked into place within the mount rings, set in the usual way for eye-relief, and then zeroed by fine adjustment of the mount - not the scope. Once the point of impact is within an inch or so, the scope turrets can then be fine-tuned for a perfect zero.

Cross-over check

It's now time to carry out that cross-over check referred to earlier, where we are hoping to see all shots falling centrally on the target throughout the entire trajectory.

Check for cross-over along the trajectory path by placing paper targets at all ranges, from 8yd back to 55yd, and fire a few shots at each range. If all the shots hold the centre-line of the target, you can ask for no more. If, however, shots stray to the right or left, on nearer or further targets other than the set zero range, then a problem may well exist. Obviously the cross-over check needs to be carried out from a stable position and, most importantly, in wind-free conditions. If those dreaded stray shots do arrive on the target, then something may be out of alignment.

The remedy depends upon the specific rifle/scope combination used. Many pre-charged pneumatics, for example, follow much the same design pattern, with a figure-of-eight clamp holding the barrel to the cylinder near the muzzle end. Slackening off the Allen screws on this clamp, even temporarily removing the clamp, may reveal the problem. With the clamp removed, the barrel is free to assume its natural position and it just may be that the barrel appears bent at this stage (in which case expert attention should be sought). More commonly, the clamp has just been tightened at the wrong point. Repositioning the clamp and re-tightening the screws, while being careful not to push the barrel from its natural course, may just rectify the cross-over problem altogether.

Some cheaper (and some not so cheap!) scopes on the market can suffer a cross-over when either the parallax or magnification rings are used, so fire the rifle from normal settings; then fire again, having made adjustments to the parallax/magnification rings, and finally gauge the results.

Finally, do bear in mind that even with a perfectly zeroed rifle there are several factors that can subsequently alter the zero:

The addition/removal of a silencer/barrel weight will more often than not have a significant effect on the zero, purely because of the change in balance/barrel dynamics etc. In my experience, the POI can alter by 3-4" at 30yd; so decide what add-ons are required and stick with it. Alternatively, have two zeroes set on the turrets, for example one zero setting with a silencer in place and another marked for when the silencer is removed.

Changing pellets, even to a different tin of the same brand, can also change the zero.

Cleaning a barrel can have a dramatic effect, but it all depends upon the barrel.

SCOPE MOUNTING GUIDE PART THREE: ALL SCOPED UP

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SCOPE MOUNTING GUIDE: ALL SCOPED UP

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SCOPE MOUNTING GUIDE PART THREE: ALL SCOPED UP

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