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Thread: Road testing the 1933 Hill pistol prototype

  1. #1
    ccdjg is offline Airgun Alchemist, Collector and Scribe
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    Road testing the 1933 Hill pistol prototype

    The reproduction of the 1933 A.H. Hill pistol described in my previous post (http://www.airgunbbs.com/showthread....tion-challenge)
    has now been put through its paces, and here is a summary of my findings.

    The cocking and loading sequence involved with this unusual two-stage cocking design can be explained by the following picture sequence.
    Pics (1) and (2): The spring loaded button on the grip edge (shown by the red arrow) is depressed, releasing the trigger guard/cocking lever. Pics (3) and (4): The cocking lever is then pulled back until it is vertical to the cylinder, at which point the sear engages the piston with a loud click. An automatic safety simultaneously locks the trigger. At this stage the hand can be released from the cocking lever. Pic (5): The cocking lever is then forced back to its original position by the palm of the hand and is locked back in place by the spring loaded button. Pic (6): The lever on the loading gate is rotated and the gate pulled outwards to access the breech. The pellet is loaded, the gate is slid back and locked in place by the cam lever, and the gun is ready to fire.







    To my relief (and surprise) the pistol cocked and fired perfectly first time. Initial testing with .177 Webley Special pellets (7.6 grain) was disappointing and power was obviously low, with an average muzzle velocity of only 150 fps. An improvement was achieved by investigating the breech seal, which was a simple leather ring, as shown in the patent. An “icing sugar test” revealed that, with a pellet in the breech, very significant air loss was occurring from the breech on firing. (This test involves daubing icing sugar over the suspected leak areas and watching for clouds of powder on firing. Icing sugar is non-hazardous and easily wiped off the gun afterwards leaving no traces). Replacing the leather washer with two rubber O-rings showed no air leakage in the icing sugar test, and the muzzle velocity increased to a more respectable 245 fps.

    Interestingly the cylinder dimensions and swept volume of the Hill pistol turned out to be almost the same as for the straight grip Webley Mark 1 pistol from the same era as the patent. The cylinder diameters of the Hill and Webley are 21mm and 20.2mm respectively, and the piston strokes are both 6.5 cm, giving a swept volume in each case of 22.5 cc. As both guns take the same size spring this meant that I could make a direct comparison between the performance of my Hill piston and a good condition 1930’s Webley Mark from my collection. In fact, in all my tests I swapped the same spring between the two pistols. The Webley gave an average muzzle velocity of over 300 fps with the above pellets, so there were obviously still some wrinkles to iron out with the Hill pistol.

    One obvious factor was the weight of the piston. As defined in the Hill patent the piston was necessarily very heavy, and mine weighed in at 106 grams, compared to only 64 grams for the Webley Mark 1. A decision was made then to skeletonise the piston to bring its weight down, and as shown in the next picture a final weight of 85 grams was achieved, still heavier than the Webley but a significant reduction.






    The pistol as described by Hill in his patent had no piston washer and relied on just metal-to-metal contact for the piston seal. Not being very confident about this I took the decision to use a simple flat leather washer to improve the seal, as shown in the previous picture. This was presumably not as good as it could be, as the Webley Mark 1 uses the more efficient cup type leather seal. So a further modification was called for and I made a seal of this type from leather, with a central PTFE retaining washer as shown next:








    With the lighter piston and improved seal there was an immediate improvement in power output, and using the tight unsized Webley Special pellets I was getting a reasonably consistent average of 310 fps (over 10 consecutive shots the variation was between 322 and 302 fps). The pellet weight was 7.6 grains, equating to a muzzle energy of 1.62 ft lbs. The Webley Mark 1 with the same spring and same swept volume gave very similar results, averaging about 312 fps with a similar spread.


    Accuracy tests were carried out using a bench rest. The following picture shows 10 consecutive shots from the Hill pistol over a distance of 6 yards.





    The next picture shows 5 consecutive shots over 11 yards.




    So accuracy and consistency seemed to be acceptable for this level of pistol.


    Having put a few hundred pellets through the gun I have now formed an opinion about the unique cocking system.
    The cocking method and automatic safety feature have so far had worked well with no problems.
    When the gun is cocked by the first outward stroke, the 14cm spring is compressed by only 4.5cm, thanks to the floating muzzle plug which at that point is now protruding from the muzzle by about 2cm. You can see this with these before and after pictures.






    As expected, this outward stroke is quite light compared with the Webley Mark 1, which at this stage would have completed its cocking action and its spring would have been compressed by 6.5cm. The trigger guard cocking lever is then pushed home, so forcing the roller unit back into the cylinder and compressing the spring a further 2 cm. The total spring compression is then 6.5cm, the same as for the Webley Mk 1. This return stroke is also easy to achieve, and although the spring is under very high compression at this stage, the curved roller system provides a high mechanical advantage. So in summary, the outward cocking stroke accounts for about 70% of the total spring compression, and the return stroke tops up by the final 30%.

    When shooting several consecutive shots, the Hill pistol is noticeably more comfortable to cock than the Webley Mark 1. However, the two steps do make it slower to use and unless one has weak muscles and really appreciates the reduced cocking effort, the time factor would offset the comfort factor for the average adult shooter. Another downside to the Hill pistol is the breech sealing system. Although this is very neat and efficient, when the gate is fully extended, access to the breech is still somewhat restricted, and inserting the pellet can be fiddly, especially if you have large fingers. As you might imagine, loading the Mark 1 is much easier.


    All in all, I preferred the Webley system, and I doubt that the Hill pistol could ever have been a serious competitor to the Webley pistols of the time. The advantages of the unique two stage cocking system over the Webley Mark 1 were not that great, and certainly would not have justified the extra manufacturing costs involved. By 1933 the Webley Senior had already been introduced, and Webley had been able to reduce the cocking effort of the Mark 1 by a much more economical means. So the Hill pistol design never came onto the market. Nevertheless it remains an ingenious and interesting part of vintage British air pistol history. It was the hardest project I have tackled, but probably the most rewarding.

  2. #2
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    Thanks for that fascinating test, John. It's amazing being able to assess the performance of a pistol that was never made. Kind of like recreating an extinct animal from its DNA preserved in a lump of amber!

    With the lighter piston the velocity is quite respectable - at least this gun was a viable proposition, function-wise, unlike your other made-from-patent creations.

    In a way this exercise just goes to underline once again what a brilliant design the Webley was, and that there's a reason behind the fact it persisted for decades and presumably made Webley a fortune in profits.

    Is there any dividend at all, accuracy-wise, I wonder, from having a fixed barrel, or did the ways Webley used to secure its barrels remove any variable from using the barrel as cocking lever?

    Thanks again. Wonderful stuff.
    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.

  3. #3
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    Hello John,

    Thanks for giving us an insight into this fascinating design which seems to have given a good account of itself after a little tweaking. The groups obtained at 6yds in particular would seem to indicate potentially consistent performance.

    This is this the sort of article well worth downloading and adding to the hardcopy archive.

    Regards
    Brian

  4. #4
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    Just read about the Hill rifle in some old AG mags and revisited this thread to check out ccdjg’s fantastic repro Hill pistol again.

    What an amazing price of work and he makes some very interesting comparisons to the Webley Mk1.

    Good stuff.

    Cheers,
    Matt

  5. #5
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    I missed this first time around. Fascinating. And utterly impressive work.

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