For some time now I've been meaning to write a post on what I've learnt from installing my Zeiss and Kahles riflescopes to Mauser's Double Square Mounts. A comment with a question on this came in overnight, so this will be my attempt to pass on some knowledge. 'What's the problem? They're just scope mounts', I hear you say. Well, there is a difference between fitting scopes to Mauser M03s with Double Square Mounts and fitting scopes with 'normal' non-quick-release mounts to 'normal' receivers.
When mounting any riflescope to any receiver the idea is to achieve a tension free installation. For example, the mounting hardware should not impart any torsion to the scope tube. Nor should the scope tube impart any torsion to the mounting hardware! Now, with a normal receiver it's not at all easy to tell if the installation job has been completed in a tension free manner. The scope and mounts are fixed on to the receiver and that's that. Job's done. Too bad if there is tension, because you can't tell. Well, not easily. Accuracy might be affected and good luck trying to figure out why. :-(
With Mauser's M03 Double Square Mounts it's easy to tell if the mounting job has resulted in torsion being imparted between the scope and the mount. It's also quite easy to avoid this happening in the first place. What I'll do is provide a list of actions for installing the scope and mounts and then describe what to look for to check if the fitment job is tension free. But first I'll outline the key point in the process, which is: to avoid introducing torsion between the scope tube and the Double Square Mount's bridge, be sure to slowly and progressively tighten all of the screws in the mounting system in a oft repeated cycle, starting with the bridge already installed and locked onto the receiver.
Tools needed:
- a small profile Torx size T20 screwdriver, or T20 bit fitted to a long shafted handle. This is for tightening the two bridge to ring-base screws.
- a small profile Torx size T10 screwdriver, for tightening the eight ring-top screws.
- optional - a torque screwdriver for final torquing of the screws. Using fingers and judgement can be just as good.
- start by resting the stock and receiver (with magazine removed) on a pair of steady sandbags or the like. I left the barrel installed, for better balance and to ensure the receiver was tensioned in its ready-to-fire state. It's handy to have the receiver positioned so that the butt is at the end of a bench, to make it easy to rest a shoulder against the butt to check eye-relief once the scope is lying loosely in the bottom rings. Best not to be picking the rifle up at this point.
- starting with the Double Square Mount's bridge and scope rings disassembled, apply a small (tiny) amount of grease to the leading edges of the bridge's swivelling cloverleaves and to the circular mating surfaces above them. Do the same to the corresponding surfaces in the mounting recesses of the receiver. Settle the bridge onto the receiver. Before using the locking arms, check that the fit of the bridge to the receiver is even and flush at both ends, with no light gaps visible. Put a white card or envelope behind to help reveal any gaps. There shouldn't be any. A little pressure with your hand might be needed to settle the bridge into place properly and to hold it against the receiver. If there's gaps, that bridge is wonky. I doubt you'll have a problem though. Close the locking arms. I try to do mine bit by bit at both ends, but I don't think it really matters if you do one all the way, then the other. If you want you can try to avoid marring the surface finish on the side of the square mounts where the locking tabs rub before snapping into their recesses. Hold their tips away from the sides of the bridge. Or you can create some patina that comes from experienced hands using quality equipment, leaving tell-tale marks that show how much the gear has been enjoyed over the years. :-)
- use the two bridge to ring-base screws (size T20 heads) to lightly attach the ring-bases. They should still be free to swivel a little. Given that the bridge is already mounted onto the receiver, reach with the T20 screwdriver up through the magazine-well. Be careful not to scratch the walnut around the magazine-well opening. Do not apply lubricant to the screws. To avoid damage to the screw fittings (or to the scope tube from over tightening the ring screws), torque settings should be achieved with unlubricated, metal to metal screw thread contact.
- make sure the ring-bases are at a right angle to the bridge and gently lower the scope tubes onto them. Try to avoid rotating or sliding the scope once it's in position. The edges of the rings feel sharp, but they are not burred. If positional adjustment is needed, gently lift the scope slightly free of the rings. Try to get the crosshairs lined up close to horizontal and vertical, for final adjustment later on. The pictures in this post (one of which is copied below) show that I position my scopes so that the end of the ocular lens is above the bottom of the dip in the stock's grip. This might work for you too. The idea is to have the scope in the right place so that when the rifle is lifted to the shoulder the full image circle is visible without needing to crane the head forward. Or move it back - getting whacked on the eyebrow is no fun.
 |
Note how the end of the ocular lens is above the dip in the stock's grip. Works for me.
|
- to get the reticle aligned, sit on a low stool behind the rifle with your eye at bore height. To keep your head steady, rest your nose and cheekbone against the stock and butt. Look through the bore until the circles of the near and far end of the bore are concentric. Now look up at the scope. There should be just a sliver of illumination showing in the ocular lens, with the top of the vertical crosshair near the middle of it. Keep switching your eye from the bore to the lens and if necessary, carefully and gently rotate the scope in the ring-bases until the top end of the crosshair is centred. If there's any resistance while rotating the scope tube, lift it slightly.
- place the ring-tops on the scope tubes above the ring-bases and adjust them so that the gaps between the tops and bases are even at both sides. Drop the eight screws (size T10 heads) into position. Use the T10 screwdriver to get the screws engaged with the threads of the ring-bases, but don't apply any tension yet. Check again that the side gaps between the rings are even. Look down at the screws and give them all a number, moving from left to right and down the length of the scope. The screw at top-left will be 1, the screw at top-right will be 2, ... , the screw at bottom left will be 7 and the screw at bottom right will be 8. We'll call the T20 screws under the bridge A and B.
 |
| Mauser M03 Double Square Mount - numbering the screws for the tightening pattern, described below. |
- now that the weight of the scope is keeping the ring-bases at a right angle to the bridge, it's time to apply the slightest amount of tension to screws A and B. Barely snug them up this first time, while pushing down a little on the scope to keep the ring-bases from rotating
- then, start applying the slightest amount of tension to each ring screw, in a pattern that will ensure the scope is not rotated in the rings by tightening one screw or another too much. Use the following order for the first round, again, with only the slightest amount of tension being applied. 1, 4, 5, 8, 2, 3, 6, 7. Then add a touch more tension to A and B, while pushing down gently on the scope again.
- repeat this cycle with screws 1 through to 8 and A and B several times, slowly and progressively increasing the tension. It might take twenty cycles if you go gently and slowly. Screws A and B are likely to start feeling a bit tight more quickly than screws 1 to 8. That's expected, but try to reach the end of tightening for all screws at the same time, noting the different torque settings described in the dot-point below. Keep checking that the side gaps between the rings are narrowing evenly. There should be about a millimetre of gap remaining at the end of tightening.
- I couldn't find any guidance from Mauser or the scope manufacturers on torque settings for these screws, so settled on settings listed by other manufacturers that looked right and matched my previous experience. I finished the tightening sequence when I had reached 2 Nm for the ring screws (1 to 8) and 4 Nm for the bridge to ring-base screws (A and B). These settings are close to 18 lb/in and 35 lb/in respectively. For the ring screws 1 to 8, this is not particularly tight and is comfortably achieved by firm finger tightening with a screwdriver. For the bridge to ring-base screws A and B, it's more of a firm hand hold on the screwdriver. Depending on your setup and tools, the final tightening of A and B might be done once the mounts and scope are off the receiver, as reaching up with a tool through the magazine-well is a bit awkward. There is no need to use a wrench to get more leverage on any of these screws! I'm going to suggest that you avoid using a torque wrench, even a very small one (and even though I did at first). These wrenches are not very accurate, particularly at the lower end of their ranges. It's too easy to turn a screw too tight, waiting for the click, with insufficient feel for how tight things are getting. I was very careful when using my little torque wrench that one time, but didn't enjoy the lack of feel. Better to rely on the nerves in your hands, or a trusted, quality, light duty torque screwdriver, that preferably has the setting that's needed in the middle to top half of its adjustment range. If I keep getting older (probable) and keep losing the fine sensation of touch in my fingers (possible) I might have to treat myself to this nice set of torque screwdrivers from Wera in Germany. :-) (who have since advised me that these tools are made next door in the Czech Republic. That's OK - the Czechs have a fine history of quality manufacturing.)
Checking for Torsion.
- once all of the screws have been tightened, unlock the Double Square Mount's locking levers. As with locking these levers, I try to unlock mine progressively at both ends, so that one isn't completely loose while the other is completely tight, but it probably doesn't matter. Lift the scope and mounts off the receiver and then carefully lower them back into place again. Let the mount settle on the receiver, with a little push if needed, but don't swing the locking arms. Use the white card or envelope in good light to see if there are any air gaps between the mount bases and the receiver. There should be nothing to see. Check to feel if there is any side to side rocking of the mount bases on the receiver. There shouldn't be any. If there is it's caused by the front and rear rings having been tightened onto the scope tubes slightly rotated relative to each other. This can happen if the ring and base screws were not tightened in the gentle, progressive and cyclical manner described in the dot-points above. Chances are no harm has been done; simply loosen all the screws progressively, starting with A and B first, then 1 to 8, and start the mounting process again, being more careful this time. :-) However, I'm anticipating that if the instructions listed above have been followed, there'll be no problems.
Lastly, please respond with a blog comment or a forum post to let us all know how you get on. If your scopes have already been installed into Double Square Mounts, are you feeling any rocking of the mount bases on the receiver, or seeing any light gaps?
