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'scope mounts and damage to dovetails / 'scope tubes

Discussion in 'Anything Airgun Related' started by cloverleaf, Sep 6, 2014.

  1. cloverleaf

    cloverleaf Honorary Member

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    Over the years I've seen many examples of 'scope mounting dovetail rails and 'scope tubes that have been damaged by over-zealous meatheads hanging off the Allen keys when fitting 'scope mounts.


    Dovetails / Rails


    While not exclusively affecting PCPs, this problem is usually far more likely / severe on the many PCP rifles with aluminium action blocks (and dovetails) - I've seen many damaged Air Arms 400 Series blocks, but also HW100s, Daystates... funnily enough I've never seen any BSAs with damaged rails - maybe because their blocks are extruded (and hence stronger), the rails are wider (not sure how this would help, though) or the finish is that poor that damage isn't easily distinguishable :p

    As already mentioned I've always considered damage of this sort to be the preserve of the ham-fisted, ill-educated shooter who doesn't really know how to fit a 'scope properly. Unfortunately, I've since noticed less-severe examples of such damage on my own guns (HW100 and S400) despite my persistent intention to be as gentle as possible when tightening 'scope mounts :eek:

    I've also noticed that (while it may be coincidence) the recent damage on two new guns has been when they have been fitted with 30mm tubed 'scopes. This would perhaps figure to an extent; since, for a consistant 1.5mm wall thickness, the tube of a 30mm 'scope will be
    around 70% stiffer than that with a 1" (25.4mm) tube - meaning that the tube will be far less yielding and accomodating of any alignment issues in the mounts - putting additional load on the dovetails.

    In addition I've noticed that the clamp profile of Sportsmatch mounts doesn't necessarily suit certain dovetails (which is hardly surprising, given the lack of standardisation across makes) which reduces contact area between mating faces; potentially increasing localised stress.


    'scope Tubes

    Marking on 'scope tubes is also very common too - I find it ranges from light marks on the finish (that can be visually detected if not by touch) around the edges of the cradels / straps near the mounting bolts, to significant and obvious deformation and crimping if someone has really gone apeshit in the past. Try as I might, I find it very difficult to mount a 'scope without marking the tube to some, small extent.


    So, what can we do to avoid this damage?

    Several things spring to mind when attempting to minimise damage to 'scope rails:

    Use as little clamping force as necessary -
    An obvious one, but worth stating none the less. Apply as little torque to the clamping bolts as possible, while still allowing the 'scope to be mounted securely.

    Use as much clamping area as possible - Ideally one-piece mounts are a good idea (I always use them on HW springers now, due to damage to the dovetails), although these can't often be used on PCPs. In this case, stick to wide two-piece mounts, and avoid skinny "economy" types.

    Use a clamp profile that suits your rail - As previously mentioned, I've found that Sportsmatch mounts don't offer a lot of contact area at their contact point with some rails - others (such as the long-discontinued B-Square and Hawke adjustable offerings) seem to have a far better defined clamp profile.

    Use a clamp size that suits your rail - We all know that dovetail rail sizes vary across manufacturers (for example, BSA are notorious for using wider rails than anyone else) using mounts that are the wrong size for your rails is a sure way to cause damage.

    Use "self aligning" mounts with a gimble - Some mounts (the B-Square items mentioned above) have the 'scope cradles mounted to the clamp bases via a floating gimble assembly - this allows the cradles to rotate with respect to their clamp bases; removing the possibility for alignment issues between 'scope, mount and rail generating excessive stress in any of these components.

    Consider using 'scopes with 1" tubes rather than 30mm - Based on the previous stiffness / alignment / stress argument, I suspect smaller OD tubes will cause less damage to mount rails.


    In addition, it would be helpful if manufacturers of guns and mounts agreed on a standardised rail size and format (like that's ever going to happen :rolleyes:) and if rifle manufacturers used steel instead of alloy rails (perhaps bolt-on units).


    As regards damage to 'scope tubes, solutions are potentially a bit more difficult. Every set of rings I've used for airguns has marked the tube to some degree. There are some mounts available (usually cheaper ones) with adhesive strips inside the rings; designed to separate the ring from the 'scope body. In the past I've just dismissed these as a lash-up to get around alignment issues caused by poor QC; however I'm now wondering if they have a point. If so, why haven't the higher-end manufacturers (Sportsmatch) gone this way too?

    Another option is a system like the Sako Optilock - which uses a split, synthetic insert between the rings and 'scope; acting both as a gimble to minimse alignment problems and also as a cushion between the surfaces of the rings and tube. Can't see many airgun shooter spunking £100 a set on similar, though.

    Some may not see this as a problem, however having recently acquired several sodding expensive (by my standards), definitely-not-disposible 'scopes I'm extremely loathe to fit them to owt, knowing that (no matter how careful I am) after being shunted from one rifle to another they'll end up looking like the proverbial dog's dinner - covered in clamp marks along the length of their tubes :down:


    If anyone has any thoughts on this issue, I'd be interested to hear them :)
     
    Last edited: Sep 6, 2014
  2. bf95

    bf95 Donator

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    I have often wondered about the adhesive tape on the cheaper mounts and if it does help protect them from visual damage, I wonder if that is thin adhesive foam will act as a shield but without causing other problems such as miss-Allignment or canting. As for the standard mount dimensions and materials I don't see why not, I may be wrong but if I remember rightly that's where the pirating came from, with the indiscepacies with the weaver style rails
     
  3. Jackal

    Jackal Posting Addict

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    Get the mounts 'lapped', it's surprising how much comes 'off' to make them truly square!

    They'll probably need to stay with the gun rather than the scope.
     
  4. terry1001

    terry1001 Major Poster

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    I've fitted a few scopes over the years and have never suffered any damage to the scope tubes or even any marks and certainly no damage to the rifle dovetails. I don't spend a lot on mounts either these days as pcp rifles don't generate as much recoil as full bore centre fires or springers but I do look out for solidly made mounts with double screw fixing. Decent picatinny rails are a much better system for mounting scopes plus anything else (in my opinion).
    Allen keys are not meant to be used with long extension bars to tighten them up, like spanners they're made in an appropriate length to be done up by hand.
    The method I use to mount a scope is to sort out where the mounts have to be fitted to get correct eye relief, clearance for loading etc and then I fit the scope mount bases in position making sure that they fit nicely on the rifle. At this point I then lay the scope in the rings and make sure that it fits properly which checks that the mounts are correctly aligned as the scope should rotate and slide backwards and forwards smoothly and cleanly. I then roughly square the scope up to get the reticle aligned and the eye relief right and lightly fit the upper part of the rings prior to confirming the scope position while it can still be moved. When I'm happy with this I tighten the screws evenly making sure that the top of the ring has an equal gap to the bottom part on both sides, I start by nipping down the first screw until it starts to move the ring and then do the same to the one which is diagonally opposite. Next on to the one on the same side and then the one diagonally opposite that which means that all 4 have been nipped up, repeating this procedure until all four are snugly tightened.
    Any shimming will cause uneven stresses to develop somewhere in the mounting system/scope tube and can cause damage. If I did ever have the need to physically adjust the body of the scope relative to the dovetail I would use either adjustable mounts or, for my own gun, I would bore a set of mounts to the correct angle to get perfect alignment.
    Using damaged or poorly fitting allen keys can also cause you to slip and scratch scope or rifle.
    Before fitting the rings it's good practice to degrease the dovetails and the mount bases to make sure that there is no oil or dirt to interfere with fitting and also to just try fit the mounts to make sure that they are the correct size and angle to fit properly. As mentioned some mounts do have small pads of sticky tape on both halves, I don't know what the purpose of this is as they seem too small to offer any cushioning but they do help stick the scope in place until the rings are tight. If I think about it I usually remove it and I have sometimes used masking tape to line the rings which is just stuck to the curved surface and then trimmed all round with a craft knife so that it doesn't show when the mounts are fitted. This tape does, I believe, have enough 'give' to accommodate very slight misalignment or marks on the surface but will allow the rings to be fully clamped in position.
     
  5. Sir Oscar

    Sir Oscar Donator

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    How are you doing this lapping square?
     
  6. Stevie Darling

    Stevie Darling Sexual tyrannosaurus

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    For inside the scope ring I use tennis racket tape, this tends to be just a tad wider than a double strap ring so doesn't look out of place.

    The tape also creates more grip between 2 smooth surfaces reducing the need to go mad with the alen key.

    I would much much prefer to see weaver rails used instead if dovetails, as there is more mounting options, and a more secure scope, again no need to go mental with the torque:)
     
  7. Jackal

    Jackal Posting Addict

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  8. cloverleaf

    cloverleaf Honorary Member

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    Thanks guys :)

    Jackal - hadn't thought of lapping the mounts; although I can see a few issues. Must firearms mounts are blued or stainless steel; so can be lapped with relative ease. Obviously our mounts are mostly anodised ally - so far harder to lap in the first place and very difficult to refinish once cut. Nice idea though - would certainly ensure perfect alignment.

    Terry - good work; do you use any 30mm tubes though? I use exactly the same mounting procedure as you (with the exception of degreasing the rails); following this experience I've vaguely tempted to invest in a small 1/4" drive torque wrench for doing mounts - would certainly ensure that everything was tightened consistently and to a know value. The electrical tape sounds like a good idea; although I'm not sure what sort of thickness it would add to the whole setup - obviously this can be accomodated in the vertical plane by displacement of the top straps; not in the horizontal plane, though.

    Stevie - crikey - is that not a bit thick? What sort of thickness does the tape squash down to when the mounts are tightened?


    Following this little escapade, I'm wondering if I should spunk some more money on Hawke adjustable mounts before they become extinct!
     
  9. Stevie Darling

    Stevie Darling Sexual tyrannosaurus

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    Its only as thick as probably doubled up leccy tape, maybe cheaper stuff:D

    Using sportsmatch mounts, it fits perfectly. The bolts are nipped up just to get a grip, tryed and tested on a BSA lightning with a kick like a horse, scope has not moved with no loss of zero.
     
  10. Patrick

    Patrick Donator

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    When I mount a scope I first check the inside of the mounts(where the scope sits) to make sure there are no imperfections and that they're nice and smooth. I then had a layer of masking tape to the inside of the mounts to prevent any marking of the scope tube.Using masking tape also tells you how good the contact is between scope and mounts because it will show up in how well and even the tape is compressed.If there is any uneveness you could use use some strips of very thin rubber( such as rubber from a balloon) on the inside of the mounts to compensate for this.
     
    Last edited: Sep 7, 2014
  11. terry1001

    terry1001 Major Poster

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    I only have a Photon in 30mm at the moment although I've used some previously - still not sure whether they gather more light than a 1" everything else being equal.
    Although I've not actually done it yet I sometimes think that running a tap though the fixing holes might be a good idea as some are definitely a bit tighter than others, certainly would be worthwhile if you're ging to use a torque wrench.
    Lapping with aluminium rings/mounts would be difficult as the 2 parts of the ring don't normally meet but it would be possible to make up a tool to do it if it were necessary although I'm not sure that the benefits would be worth the effort in most cases. The alignment of the lower halves can be checked with a steel bar/tube of the correct diameter or even the scope itself and if you use a steel bar it could be coated with an abrasive paste and working the bar gently backwards and forwards through the rings it would align and size the aluminium rings but this would need to be done very carefully and checked after every few cycles to make sure that the minimum of metal is removed. using a very fine paste would be better and should leave a decent finish.
     
  12. mark112

    mark112 Engaging Member

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    Hi

    Think I have something (i.e an adjustable 1/4" drive torque screwdriver thingy) in the deep recesses of the garage you can have if it's any use Mike. Will try to dig it out tomorrow. I would look tonight but it means negotiating the Censored laden minefield that my cats think is for their own personal 'convenience'. I thought that cats don't crap on their own doorsteps .... mine do! [/END FELINE RANT]

    Mark
     
  13. ratman60

    ratman60 Pro Poster

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    hello, yes once again an excellent read and some good advice and technical terms, i had my photon fitted by the gunsmith on the T12 and so far it has been ok, your right though a 30mm tubed scope or n/v fitted to the narrow rail of most PCPs or springers needs carefull placement than the 25mm but both need fitting correctly. i agree with terry to as i go for the mount to eye relief way.
     
  14. 177

    177 Donator

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    My mate uses a thin strip of mountain bike inner tube (about 1/4 of an inch wide in real money :rolleyes: ) on both the top and bottom of his mounts, and minimal pressure when tightening. He swears by it - I have to admit, it does appear to work extremely well. The rubber compresses slightly under pressure and appears to 'grip' the scope body very well. Similar in principle to using 30mm mounts with inserts to hold a 1" or 25mm scope body I suppose.

    When I fitted my 30mm Leupold VX2 onto my .270 my backside was nipping at my shirt tales just a tad ;)

    Expensive mounts reassured me to a degree and the scope is unmarked (I've checked :eek: ).
     
  15. sharpsman

    sharpsman Pro Poster

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    Fortunetaly my scopes are undamaged form my mounts, but i have seen a fair few high end scopes that have been badly marked by ham fisted people - why people think they have to keep tightening the bolts until they strip them or can not tighten them anymore is beyond me.
     
  16. mattyts

    mattyts Donator

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    I think one of the big problems is long handled allen keys,I have a set of Wera stainless allen keys in both metric and imperial,they are great tools but the handles are so long,it's hard to determine how much torque you're applying so I've found for mounts,it's much safer to use regular allen keys.
     

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