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Thread: The Webley Mercury pistol saga continued. Part 2.

  1. #1
    ccdjg is offline Airgun Alchemist, Collector and Scribe
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    The Webley Mercury pistol saga continued. Part 2.

    In Part 1 of this series of threads on scratch-building a copy of the Webley Mercury pistol, I had got as far as making the basic frame, cylinder and barrel components:





    Since then I have been carrying on with the project (among other things), during lockdown and thought now would be good time for an update on progress for those of you who expressed an interest in the project.

    The next phase after building the basic carcase was to make the working parts of the pistol: the cocking links, piston, trigger and sear. But first I had to decipher the patent, as like most patents it was a bit short on detail. This can be the fun part of a project like this, trying to work out exactly what the drawings represent and how the mechanism actually works. Quite often there are things in the drawings that are not mentioned in the text, and just when you have decided that they are irrelevant and you leave them out of the build ,you find that they are important after all. Sometimes you can see important things in the drawings that are unclear, but there is no helpful description in the text, so you have to work things out for yourself. A good example in this case of this is the shortest of the three cocking links in this part of the drawing, marked as No 21, which the patent calls a “pawl”.(I looked it up and ‘pawl’ is as good a description as any).







    This has to press firmly in the notches in the piston during the two cocking strokes (items 22 and 23 in the drawing), but then has to be set free when the barrel is returned home. The patent describes it as “spring-loaded” but there is no indication of the design of the pawl or what sort of spring is used or how it is fitted into the pawl. In the end I took inspiration from the short cocking link used in Webley pistols, such as the Senior and Hurricane, and made it as follows:






    Once made and fettled a bit, it seemed to work well, so it must have been along the right lines. It was milled from carbon steel, so that it could then be heat hardened, which is important as it is going to have to take a lot of stress and wear. The long and short cocking links (items 19 and 20 in the above drawing) were also made from carbon steel for strength, using bar of 5mm thickness. This makes for harder work cutting and filing, but it is worth it in the long run for components that are subjected to a lot of stress. These links needed to be a sliding fit in the channel that had already been milled into the steel frame. Then all three components could be pinned together and the whole unit checked for free travel when attached to the barrel.
    I should point out that I am making the second version of the Mercury, not the first which is the one in the patent, and there are a few unknowns to deal with. I only have one photograph of the second version to work with (and a knowledge of its barrel length), and it was clear from the start that some of the external dimensions were slightly different from the patent version, and also that there would be some minor differences in the internal layout. This meant I could not just work straight from the patent drawings, and a lot more thought had to go into working out dimensions and the relative positioning of moving parts.
    This was particularly true in the case of the cocking link train and the piston. The cocking link train had to be an optimum length to maximise piston movement, and the positions of the two cocking notches and two sear-engaging notches on the piston also had to be precisely spaced for the whole cocking process to work. All this caused me a lot of head scratching but I finally came up with what I thought was a reasonable compromise.
    Now for a confession. It’s a sad fact that, whenever I make components from carbon steel for a project, after a lot of hard work and fettling I always end up having to make at least one of the components again, and on occasion even three times. Inevitably something unforeseen crops up later down the line which makes the part unusable – too short (never too long, which would be easy to sort out), pivot hole in the wrong place, wrong shape, you name it. I always try to think ahead and anticipate these snags, but never succeed totally. So when I am sweating away hacksawing or filing a very hard steel piece, putting a lot of thought, time and effort into it, it keeps coming into my mind that this could be the one that ends up in the scrap bin. Very off-putting! And the current project was no exception. When the assembled cocking link was tested with the piston in place, it lined up exactly as shown in the patent drawing shown above. The trouble was, when the gun was cocked and fired, the piston smashed into the spring-loaded pawl, which was protruding into the cylinder (it was being held there under the action of its spring). The patent diagram, which shows the pistol in the uncocked or fired state, was obviously incorrect. Just my luck. It should have shown the pawl sitting slightly ahead of the piston notch, so that it had ridden up against the end of the cylinder slot and had been lifted out of the cylinder cavity. That way, the gun could be fired without damaging the pawl and/or the piston head.
    So despite all my best intentions, the cocking link train I had so carefully made needed to be shortened by about 5mm, and as the short and long links had already been drilled and profiled, the only way I could do this without weakening the linkage was to make a new short link, 5mm shorter than the original. So it was back to the hacksaw and file So the cocking linkage pictured in the next group of pictures is actually my second attempt.




    You can see from the next pic how the linkage looks when fixed to the barrel and cylinder. When the cylinder is eventually fixed to the grip frame, the linkage will sit in a channel in the frame and the spring-load pawl will be pressed flat against the cylinder.




    With the cocking linkage made, attention could then be turned to the piston. I have found that the simplest way to make a piston is to use steel tubing that is a loose sliding fit in the cylinder and then to block one end with a steel plug. This requires a lot less effort than boring out a steel round bar, especially if tubing of the right diameter can be bought. In this case my cylinder had an internal diameter of 25 mm, and 25m tubing suitable for the piston was readily available on the net. The plug for the piston head was turned down from steel bar until it was slightly oversize to fit inside the tubing. The tube was heated to a dull red heat and the plug tapped in place. As a belt-and -braces way of further securing the head in place, three holes were drilled into the head from the side, tight fitting steel pins hammered in, and then the excess cut off and the pins filed flush . The head was then drilled and tapped to allow a piston seal to be fitted.

    As a first stab at a piston seal, I decided to use PTFE rod, and to turn one down on the lathe. I have never used a PTFE seal in my repro’ pistols before,as leather was always more appropriate. Anyone any thoughts on PTFE versus leather? Anyway, I will give it a try and if I am not happy with it, I can always go back to leather.

    The final parachute-style seal was fitted to the piston with a countersunk 2BA screw and washer. The final piston was a close sliding fit in the cylinder, and when pushed down hard into the cylinder, it held the compressed air well. The sequence of events in making the complete piston is summarised in the following pics. (Note that the actual thickness of the plug used to form the piston head was about one half of that shown in the first frame).







    The piston once made then had to be cut with four notches: two to receive the spring-loaded cocking pawl, one for each cocking stroke, and two for catching on the sear after each cocking stroke. It is interesting to see how the double cocking action works, and you can understand this from the following drawings.






    The piston notches shown in red and labelled as A1 and A2 are the ones that the cocking pawl locks into. The notches shown in blue, labelled B1 and B2 are those intercepted by the sear.
    (1) shows the gun before cocking. (2) shows the first cocking stroke, where the cocking pawl has connected with notch A1 and pushed the piston back until it is held by the sear in notch B1. The barrel is then returned home to give situation (3). The piston is now cocked in the first stage, and if wanted, the gun could be fired for a low-power shot. When the barrel is pulled back again for the second stroke, the pawl engages with notch A2, as shown in (4) and the piston is pushed back again until the sear engages with notch B2, giving situation (5). The barrel is then returned home, as in (6) and the gun is now ready to fire on full power.



    As you might imagine, the relative positioning of these notches is critical for the gun to cock properly, and also to take full advantage of the available swing of the barrel to ensure a maximum swept volume. Also the angle of the notches was important to ensure that no slippage might occur during cocking. Needless to say, this stage caused a lot of puzzling out and modelling with cardboard cut-outs before committing the piston to notching. When I was reasonably confident that I had the layout correct, the piston notches were then milled in and it was with huge relief that a trial run showed that all was OK.
    The piston also needed a slot milling along its top, exactly opposite the train of notches, so that a screw protruding through the cylinder wall would ride in the slot and so would keep the piston notches always in line with the cocking pawl and the sear. If this feature was omitted, the piston could rotate out of line with continuous use of the gun, and the gun would then fail to cock. The only recourse would then be to disassemble everything and realign the piston, not something you would want to do after every dozen shots or so. The patent makes no mention of this feature in the text, but once I realised it had to be there, I was able to find it the patent drawings, with its guiding screw. The lower picture shows the guide slot.




    The next step was to make the trigger and sear pieces. I used the same 5mm carbon steel plate that I used for the cocking links. Although this made hacksawing and filing harder than if I had used mild steel, it did mean I could heat harden them once finished and they would stand up much better to wear and tear. This was particularly important for the sear. This is the sequence in making them. They were first made oversize and only roughly shaped, and with the holes for the pivot pins also drilled, they could then be fitted onto the frame with the pins and then sized and shaped more accurately. The long arm of the sear lever was also drilled with a hole for attaching a spring. The last picture in the sequence shows the trigger and sear in place, with the sear spring fitted.





    Now was the moment of truth, as I had all the necessary bits to assemble the working parts of the gun and to see if the gun actually cocked and fired. So using a weak main spring (as I did not want to put the load bearing parts under much stress until they had been hardened) the gun was assembled:




    With bated breath I broke the barrel and cocked the gun. Yes, the pawl picked up the first piston notch OK and pushed the piston back until there was the reassuring click of the sear engaging. The gun had successfully achieved the first cocking stage! I then returned the barrel home and re-cocked the gun. Yes, the pawl picked up the second notch and pushed the piston further, but disaster! Everything came to a dead stop and there was no way I could get the sear to engage with the second notch. So the gun was taken apart and checked. The notch distances seemed OK, there was nothing obstructing the cocking links in their channel, and nothing blocking the trigger or sear movement in the second stroke. What the hell could it be? After reassembling and hitting the same problem again, I agonised over the problem, untiI I realised what an idiot I was. When I made the piston, I deliberately made it a bit longer than necessary so that I could trim it to an optimum length later on. I had forgotten this. It turned out that it was just that bit too long and was hitting the end of the cylinder in the second cocking stroke, before the notch could engage with the sear. So out came the hacksaw and with 5 mm trimmed off the end of the piston, the gun worked perfectly, at least under very light spring load. The sear now engaged after both cocking strokes, and the trigger worked fine so that the gun could be fired after the first or second cocking stroke. Testing the action proper with powerful springs would have to wait until the rest of the gun was finished and all the relevant parts heat hardened. This would include case hardening the piston, as it was made of mild steel and the notches would become rounded, and pretty soon useless, if some protective measure wasn’t put in place.


    The next aspect of the build I wanted to tackle was the “cladding” that was to go around the grip frame and help make the pistol begin to resemble the original prototype more closely. I had decided that the cladding would consist of two aluminium panels screwed to each side of the frame. Aluminium was chosen, as it would not add too much extra weight to what was already promising to be a heavy pistol, and also it would go some way to representing the aluminium alloy casting that the prototype was (presumed to be) made of.

    The following pictures show the processes involved in making and fitting the side plates. Each plate was profiled to give a snug fit against the curvature of the cylinder, but their inner surfaces were milled out in steps so that their weight was reduced as much as possible. The plates were then drilled and screwed into tapped holes in the frame.



    So that is where I am up to right now. There is still quite a way to go, including making the grip plates, trigger adjuster, safety catch, and front sight. Fortunately the rear sight used on the original prototype Mercury (second version) was the same as the Webley sight used on the Hurricane pistol and other Webley airguns of the period, and as I happen to have one of these (which I snapped up on this forum recently) that will help save me some time.
    Once all the parts have been made, fitted and polished. I will then have to etch the lettering on the gun, blue the steel parts, and anodise and black the aluminium cladding. Only then will I put the gun through its paces, experimenting with different strength springs (the prototype used two concentric springs), piston seals, transfer ports etc. It will be interesting to see how the gun performs and how effective the double cocking action is. All will be reported in Part 3 of this mini-marathon, unless of course the gun completely disintegrates on its first serious outing.
    Last edited by ccdjg; 10-08-2020 at 06:58 PM.

  2. #2
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    John, you never cease to amaze me. A very informative narrative on the status of your Mercury. I really enjoyed reading your write-up while having my morning coffee. I am not mechanically inclined and have difficulty putting a Haenel Mod 28 back together once I have taken it apart.

    Looking forward to seeing the final project.

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    Fantastic entertainment! Thank you for being so candid about your trial and error process. It gives hope to all of us 'plodders' in life, not that we would have the guts or persistence to take on a project so complex!

    The pawl reminds me a bit of the safety sear in the Webley Service, which is moved clear of the piston when the barrel is returned after cocking. Although unlike this pawl it has no actual function in the cocking process.
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    micky2 is offline The collector formerly known as micky
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    What a labor of love, and something l would not have the clue how to start doing. l take my hat off to you. roll on to seeing the finished pistol and how it performs.

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    Thanks for posting. I enjoyed seeing your work.

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    very good mate

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    John--How do the dimensions of the pistol cylinder and barrel compare to a Milbro Cougar?
    With that lumpy cylinder and plug it reminds me of a cougar but without the big lump of breech block stuck up over the top of the barrel.

    Also that frame and trigger mechanism looks like the way that Milbro should have gone with the Cougar.

    Theres another project ---how the Cougar should have been


    I hope you get the gun finished and it plinks really well.
    Last edited by ggggr; 10-06-2020 at 04:28 PM.

  8. #8
    ccdjg is offline Airgun Alchemist, Collector and Scribe
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    Quote Originally Posted by ggggr View Post
    John--How do the dimensions of the pistol cylinder and barrel compare to a Milbro Cougar?
    Hi Guy, I had a quick look at the Cougar and the cylinder OD is almost the same as mine so I would guess that the inside diameter is going to be pretty similar, at 25mm. Looking at the piston travel (very approx.) this gives a swept volume of about 34 cc. My Mercury has a swept volume of 27 cc, so it is about 20% lower.
    The Mercury barrel is 170mm long, the Cougar is 200mm (real barrel, not the fake outer).
    So I am not expecting mine to be as powerful as the Cougar, but then again I will be able to use a stronger spring because of the double cocking stroke. It will be interesting to see how much power I can squeeze out of it.

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    This is great. Wish I had 1% of those skills.

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    awesome work...
    I'm currently looking for: pair of scope low/med 25mm mounts to suit a 13mm BSA rail, any thin drinking straw barrels (any cal), and any cheap, interesting, knackered project guns. Thanks, JB.

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    I've added inks in the gallery to John's previous projects. It's a very impressive body of handiwork so far!



    Lincoln Jeffries patent pistol
    Haenel Sport Modell 55R
    Frank Clarke twist grip
    Webley Whiting
    Hill patent pistol









    Last edited by Garvin; 12-06-2020 at 08:04 PM.
    Vintage Airguns Gallery
    ..Above link posted with permission from Gareth W-B
    In British slang an anorak is a person who has a very strong interest in niche subjects.

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    ccdjg is offline Airgun Alchemist, Collector and Scribe
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    Thanks for putting those pics and links up, Danny, and for sorting the pictures out. There are another two guns somewhere, and this Mercury will be the eighth I've made when it is finished.
    I think I'll hang my hacksaw up when I get to 10.
    Last edited by ccdjg; 12-06-2020 at 09:47 PM.

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    Quote Originally Posted by ccdjg View Post
    Thank for putting those pics and links up, Danny, but I can't take credit for the guns shown in pics 4 & 5 as they were made by other hobbyists (the twist -grip was made by Mac Evans and the Webley Whiting by Leonard Joe). The correct pics of my efforts are in the links though.

    Mac had a slightly different take on the visual appearance of the twist-grip than I had, and his gun predates mine by several years. Len's Webley Whiting looks virtually identical to mine but is constructionally superior in certain respects.
    Corrected.
    Vintage Airguns Gallery
    ..Above link posted with permission from Gareth W-B
    In British slang an anorak is a person who has a very strong interest in niche subjects.

  14. #14
    ccdjg is offline Airgun Alchemist, Collector and Scribe
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    It has been more than a month since I last posted, so in case some of you who have been following this thread are wondering what has been happening, here is a quick update.

    Everything was going well until it came to milling a slot in the barrel for the front sight. I took meticulous care in appropriately clamping the barrel/barel housing unit in the lathe (difficult due to its awkward profile) and ensuring that the slot would be perfectly aligned with the barrel sight line. I was also very careful to ensure that the slot did not go too deep and penetrate the bore. Unfortunately I was so preoccupied with these details that I didn't spot the elephant in the room. The milling was proceeding slowly and smoothly and I was starting to congratulate myself on a tricky step completed, when I realised that I was milling the slot on the underside of the barrel. I won't bore you with the details of what went through my head, or what I said at the time, but it wasn't "Oh dear me!"

    I tried to salvage the barrel housing/detent unit, but I had fixed the barrel in too well and couldn't remove the barrel without damaging the housing drastically. So I had to bite the bullet and make a complete barrel/ barrel housing/ detent all over again. Not something I relished.

    I have also had to make a new piston from scratch, as I found that the precision steel tubing I had used was just that little bit too slack in the cylinder. Normally this is not a bad thing in a springer as you only need the piston seal to be a close fit, but in this design you need maximum contact between the cocking link and the piston notch to take the cocking force. Any excessive play and the cocking link can ride out of the slot. I found that with a powerful spring in the cylinder there was a tendency for slippage and deformation of the piston slot.

    As I could not buy any steel tubing with a closer fit to my cylinder, or any with an adequate wall thickness that would let me turn it down to the right diameter, I had to make the piston the hard way, by turning down solid bar to the right diameter and then boring it out. Anyway, this has now been done and the new piston works fine, with no signs of slippage. The cocking link has been heat hardened, and the piston itself case hardened, so there should now be little wear with frequent use.

    So the gun is more or less finished, and all that remains to do is some checkering to the grips, the lettering to be etched, and the whole thing blued. When it is completely finished and its performance assessed I will put together a final account in Part 3. I must admit, I am getting to like the dual cocking action more than I thought I would.
    Last edited by ccdjg; 10-08-2020 at 06:58 PM.

  15. #15
    ccdjg is offline Airgun Alchemist, Collector and Scribe
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    Some you win, some you lose

    Well, I decided the piston was a bit too heavy and was probably keeping the power down, so I decided to get rid of some of the weight by milling slots in the sides. The piston does unfortunately have to have quite thick walls (about 3mm) compared to most other pistons, because the cocking and sear notches are milled into the wall. The thick wall more than doubles the weight compared to the pistons of similar sized pistols. My piston actually weighed in at about 185 grams, which can be compared to the mere 70 grams of the pre-War slant grip Webley Mark 1. After milling four suitably spaced slots I was able to bring the weight down to about 120 grams, and sure enough the power went up. To try and get even more weight off, I then cut a wide groove around the circumference of the piston head. This brought the weight down to 108 grams, and as that was good enough for me, I then case-hardened the piston. This process left the piston black and scaly so I did a bit of a clean up, and then suddenly the whole thing fell into two halves in my hands. I had not allowed for the conical depression inside the piston head when I cut the groove into the head. I had left only a wall of about half a millimetre thickness holding the head to the body. The case-hardening process had then made the wall brittle and probably introduced some stress fractures as well, so the whole thing was just hanging together by a thread. Needless to say I was pretty mad, and at that particular moment I was sorely tempted to throw the whole project in the bin and call it a day.


    In the following picture, (A) shows the first piston I made that proved to be too slack. (B) shows the new, perfectly functional, piston before I had cut the groove around the piston head. (C) shows the piston after grooving and case hardening, and giving up the ghost.


    After 24 hours things didn’t look so black, so I ordered some more 30mm bar and then set about making a third piston. Onwards and upwards, as they say! So I have now made another piston, and learning from my mistakes I have reduced it in weight to 118 grams without weakening it. Picture (D) shows the new third piston after case-hardening and cleaning. I have changed the PTFE seal for a leather one, which I think performs better. The new piston works really well in the pistol.





    I am only thankful that the second piston fractured when it did, and not when the gun was loaded and at full cock. I could have put a pellet through the TV or even worse!


    Although everything structural is finished, I still have to apply the lettering, black the gun and then do some accuracy/chrono testing. I will report on this in Part 3, barring any more accidents.
    Last edited by ccdjg; 10-08-2020 at 09:25 PM.

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