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Bsa Mercury

Discussion in 'Technical' started by LG2, Aug 5, 2020.

  1. LG2

    LG2 Member

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    Hi all,

    I just picked up a non-working BSA Mercury .22 for only a few quid with serial number ZC08877 which I think makes it a Mk 3. It's pretty rough cosmetically which I expected for the price. There isn't any pitting or serious rust but the stock is well worn and the blacking is quite rubbed off especially on the barrel.

    The issue is that the previous owner accidentally fired the rifle while he was breaking the barrel for loading and something has broken or seized internally. I am told that this same accident happened twice. The first time the cocking linkage cracked which he welded up. It's quite neatly done so no issues there (I hope). The second time, the piston jammed forward and this was beyond his ability to fix and as he had other rifles he didn't bother fixing it and left it disassembled in a box for three years. He's not even sure whether has got lost in that time but I had a good look and I think everything's there.

    The barrel no longer fully straightens out. The linkage moves smoothly into the fully rearward position but at a bit over 45 degrees from straight it hits the back of the piston and won't go any further.

    I'm not really familiar with this rifle's internals and was wondering if anyone knew how to diagnose the problem and fix it. I'll upload pictures if required. Does anyone know where I might get my hands on spares for this kind of thing as well? I am definitely going to replace the seals on this rifle if I can free the piston. I don't have high aspirations for it really: I'm not trying to refurbish it to showroom condition so reblacking isn't an issue for now. I just want it to shoot straight and thought it was worth a try as it was only a couple of notes and just down the road.

    Any assistance much appreciated,

    L
     
  2. LG2

    LG2 Member

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    After a closer inspection I found that the piston is not completely seized. there is a few mm of play up and down. However, from what I can see, something strange happened when it broke.

    The main cylinder has a rectangular cutout in the bottom for the cocking linkage to slide in. At the muzzle end of this cutout is a small circle, making it look something like a stretched keyhole. The end of the cocking linkage that slides inside the cylinder is flared so that it cannot escape the cutout in operation (the flared section sits on the inside of the cylinder) . I assume that the circular bit at the end is so the cocking linkage flare can be put inside the cylinder.

    The piston also has a long cutout with solid ends like a letter box. The end of the linkage also sits inside this so that when the gun is cocked the linkage compresses the spring by moving the piston towards the butt. When the barrel is moved into the straight position again, the linkage slides in the cutouts of both until the barrel locks.

    Here's the confusing part. The piston is tight inside the cylinder. Neither the piston, cylinder or linkage show visible signs of damage. There are quite a lot of metal filings stuck to the grease, but these may be long term wear or from when the previous owner ground down his welding. Despite all this, the cocking linkage has somehow jumped forward so that now it is to the butt end of the piston. It is as if it has gone clean through the back of the piston without leaving a mark. Admittedly, there's a lot of filthy black grease around which might me hiding damage, but still!

    I hope I explained that reasonably clearly, but this has got me very confused.

    Maybe I should be posting this on a phantom sighting forum as well and calling an exorcist...
     
  3. Gat Man

    Gat Man Posting Addict

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    Location:
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    Don't these have a nylon piston head that can swell and jam up?



    If it's been fired twice with the barrel open/cocked I'd expect it to be bent upwards, however subtly, and considering the other issues described I think that your old Mercury might just be a parts donor!
     
    paj likes this.
  4. LG2

    LG2 Member

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    Do you mean the barrel will be bent ?
     
  5. paj

    paj Busy Member

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    How about some pics? You need to get it completely stripped and cleaned before trying to make a full assessment. As pointed out above if it has been fired twice from the broken barrel position the barrel is likely bent.
     
  6. Gat Man

    Gat Man Posting Addict

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    Yes


    Bent upwards from the force of inertia when slamming shut after being fired with the barrel open
     
  7. steptoe2019

    steptoe2019 Posting Addict

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    Location:
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    @LG2 never give up hope on an old mercury lol i know the wife tells me i am obsessed with them , i must admit it is getting to be the only gun i think of right now .
    If the barrel is bent there are nice people on here who can straight that for you and the key hole slot you refer to is so that when you remove the barrel retaining bolt the cocking arm and barrel can slide forward and the cocking arm lifts out at the hole end .
    I know a little on these but i have never found a strip down online of these but do a hunt and ask on here someone may have one .
    Also as others have said the piston head may be jammed and the movement is the piston moving in the head if the buffer washer is damaged the head does move in and out a little .
    Try and get the pictures on and i am sure people will tell you how to fix it up , if you do scrap it i might be interested in it for spares i am trying to build a full set of mercurys in .22 and .177 , i have all in .22 other than the mk1 but this gun may be worth the spares alone
    have fun messing with it that is what it is about
     

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