Minimizing or eliminating hammer bounce on a PCP

Forums General Discussion Minimizing or eliminating hammer bounce on a PCP

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    spinj
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    Perhaps some of us are of the understanding that without a properly designed hammer-spring-valve unit, air usage becomes inefficient.  Personally, I attribute this problem to a hammer spring still having preload against the hammer even when the gun is uncocked.  I wish I were able to provide an animated  illustration of what I’m trying to explain, but since you’re all very imaginative airgunners, I think this should be sufficient.
     
    Anyway, as some of us have already seen from slow motion videos on Youtube that right after the hammer strikes the valve on a conventional PCP the valve will push it back.  And because the spring behind the hammer still has some preload against it, it will cause the hammer to rebound and smack the valve a second (or third, or more) time.  This all happens very fast, which the naked eye can’t see.  So, I think that if you are able to use a hammer spring with the correct spring tension as the one your current spring utilizes that will also put out the desired velocity but exerts no preload when the gun is uncocked, hammer bounce is impossible, or at the very least, is greatly minimized because there is no preload.  Thus, when the hammer hits the valve, it will not rebound because the hammer spring behind it has no energy (preload) to let it rebound.  
     
    My Cricket can give me over 430 consistent shots at 8 FPE (powered-down for my backyard shooting sessions).  Using the cut, low-powered spring that the gun came with, there seems to be no preload on the hammer at all when it is uncocked.  I believe this might be the reason why I am able to get that many shots.  To be fair, please note that I also tuned my regulator and valve spring to work harmoniously with the hammer spring tension.  But still, I think that the lack of (or a very little amount) of hammer spring preload on my Cricket’s current state of tune contributes significantly to the shot count.
     
    Anyway, what do you all think?  Opinions are welcome.  

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    Sheharyar
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    I totally agree on your point of view about the rebound of the H spring.
    I only own a walther and it has a good action.The action has a place for spring that would stop the hammer from rebouncing.I guess I should use a spring too.

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    badammo
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    My BSA Sportsman HV only got 10 shots per fill until I removed 1/8″ of plastic shims and backed off the hammer spring tension screw another 1/8′. The preload on the spring was awful and pinged really loud. Now it has a slight ping, gets 30 to 40 shots per fill and only reduced velocity by 50 fps to 920fps. 
      My only guess for all the preload was to get to the magic 1000 fps. It also had a report on par with 22 lr. Barrel shroud took care of report. I too would like to find a spring just a little shorter to eliminate or make the preload minimal.
    It is now what a BSA is supposed to be, a usable, accurate, powerful and quiet rifle. 

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    addertooth
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    May I suggest you read some of the Marauder forums.  They have already put forward many solutions (which are now commercially available) for hammer de-bounce.  With a 190CC air tube at 3000 PSI, I am currently getting 40 shots of 40 FPE on my modified Marauder (45 shots at 41 FPE with a heavier pellet).  Is your model, the one with the 280CC or 350CC tank?    

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    DetailKY
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    You’re exactly right. Hammer bounce kills efficiency. And as stated, the marauder forum is full of hdd (hammer debounce device) and ssg (not sure what it means but effective and easy to tune. Something spring guide maybe?) FX uses a similar system and attributes to people talking about rattling noises under the action when rifles aren’t cocked. Daystate and others have solutions as well. Whichever way you choose to go will help. Eliminating hammer bounce in a few of my rifles has rewarded me with big shot count increases and lower noise levels. The first thing I do when I start tuning a new gun is to make sure that issue is already dealt with at the factory or I do it myself. It’s actually pretty simple and I really don’t understand why this isn’t standard practice on all air rifles. Seems like the manufacturers really like bragging about shot counts but I can usually get fairly close to double the count of factory estimates for a couple bucks and a little tuning if the hammer spring comes set with preload against the hammer. Maybe we should start pressuring the manufacturers of mid level rifles to correct the issue on future models so they can write it on the box a little bigger lol. 

    Do some research and you’ll find that a few fellow air gunners are complete geniuses when it comes to getting more shots and less noise. 

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    spinj – Depending upon how many coils you removed from the stock spring, you may have significantly increased the spring rate.  For example, if there were 10 coils on the spring and you removed 2 of them, the spring rate went up 20%.  For any given spring, the spring rate is directly related to the number of coils.  Regardless, great to hear you obtained such a great shot count. 

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    spinj
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    Thanks for the responses everyone!

    Airgunshooter, you are correct about spring tension being greater as a result of cutting it.  The shortened, low-power spring that came with the Cricket was already cut.  So I had no other option but to just try it out, but I kept it in as I was extremely satisfied with the shot count.  Oh and umm, 8 FPE is enough to take out pigeons with a head, neck, or spine shot at 30 yards.  Basically, it has the same dimensions as the longer FAC spring minus its length.

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    BigTinBoat
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    “AirGunShooter”spinj – Depending upon how many coils you removed from the stock spring, you may have significantly increased the spring rate.  For example, if there were 10 coils on the spring and you removed 2 of them, the spring rate went up 20%.  For any given spring, the spring rate is directly related to the number of coils.  Regardless, great to hear you obtained such a great shot count. 
     

    
If he is now running his spring in a “negative pre-load” condition, an increase in spring rate will actually help to eliminate hammer bounce.

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    spinj
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    Bigtinboat, that also makes sense since given the spring’s tension has increased and that the energy from the hammer has been expended the spring will not rebound or compress from it.  Thus hammer bounce isn’t likely to occur.

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    HatsanHunter
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    Shorty from the GTA forums made an excel about how to find the right dimensions for a  SSS (short stiff spring) producing the same energy as your OEM long preloaded spring. 

    In my 12 ft/lbs qb79 HPA, using a SSS, I am able to get about 125 shots per fill (regged at 850) starting from 2000 psi, and I have done very little valve work. It is a sweet shooter, in fact I am shooting it right now 😄 Should get loots of pellets

    I also get that hammer noise when uncocked that FX guns get, its simply the hammer without preload moving around

     

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    Yossshooter
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    I have the same thing i have amodded 2250 on hpa and i had a heavy HS was getting like 30 shots and changed to a normal HS and im getting around 65 shots also from a 2000 psi fill dont know how many il get from a 3k fill

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    Yrrah
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    So far as I know this was the first report (11 years ago 2006) on the use of short ballistic free flight hammer springs, and combined with inner reverse wound springs, being used to improve air efficiency. Since then others have taken it up or independently arrived at the same conclusion.
    Note that shortly after that report the rifle achieved an almost unheard of efficiency of well under 10 bar-cc/ fpe or better than 1.64 fpe/cu inch.

    So you are absolutely correct in what you are assuming.
    FX has used the system for some years now – I will dig up the video I took of the adjustment gap in my FX Elite which shows how the hammer bounce is killed by the system of adjusting out any hammer spring pre-load.
    Kind regards, Harry in OZ. (Again I apologize for the avitar pic which I cannot delete).   

     Hammer springs … Long , short, doubles, anti rotators, damping ..September 21 2006 at 2:31 AM
    Yrrah  (Login Yrrah)
    YFI have been playing at making my own hammer compression springs for the last few months. An interesting exercise that firstly needed a learning curve about spring characteristics, then spring making techniques and then possible applications. By no means have I reached the limits of exploration but would like to share some initial bits and pieces.

    The vague reason for doing this was to explore the possibilities of gaining some efficiency in terms of shot number for air used at reasonably high fpe in this PCP of mine; yes the same “one and only”.

    First step was to learn something of spring anatomy and dynamics, wire characteristics and diameter, spring diameter, pitch etc., and stress strain, which I gained here directly and incidentally from Mac 1 Tim, LD, Steve NC and others… 

    Step 2 was to learn how to make compression coil springs, firstly by hand and eye; then from an old shooting mate who is still pulling down and re- building motor cycle engines at 80 years of age ….. no not of “The Fastest Indian” fame, he is a Kiwi.

    If anyone who doesn’t already know how to do it is interested I will put together a little tutorial with pics some time in the future.

    So, then the experimenting began with the Excalibre.

    http%3A%2F%2Fsmg.photobucket.com%2Fuser%2FKyogle%2Fmedia%2FExcalibre%2520hammer%2520apart_zps8scz0wvo.jpg.html%3Fsort%3D4%26o%3D246

    What have I found out so far? Well with very short springs and a “free wheeling” hammer and shooting at lower fpe, in the 20 fpe and under range, some sub 10 bar-cc/fpe figures from a 203 cc reservoir were achieved. 


     I then progressed to “double springs”. These feature a relatively stronger outer spring overlaying a relatively weaker, but sometimes over-long pre-tensioned inner spring. See above pic. The springs are wound such that the inner one is reverse wound. The theory was that this arrangement might do three things. Firstly, smooth and well centred operation may facilitate consistency. Secondly, hammer rotation may be reduced or negated to an extent. …Edit, I guess this has been thoroughly explored in spring piston air rifles in an attempt to reduce torque….. Thirdly there may be a lack of synchrony in the rebound vibrations and harmonics between the two springs that may dampen the rebound and bounce characteristics.

    Well the results so far are OK I guess, not earth shattering… with only a couple of combinations tested last trip to the farm: ….. At the reasonable power of 25.5 fpe and 850 fps average, with a 30 fps total spread, 45 shots were recorded from a 190 bar to 124 bar fill at 11.67 bar-cc/ fpe from the 203 cc reservoir. JSBs, unweighed .22 cal, nominal 15.9 gr Exact pellets. More to come.

    It’s an interest …………… Kind regards, Yrrah. 

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    Yrrah
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    I credit this video to Dan Brown who responded to a post of my video of the FX Elite with a better one of the FX Independence hammer strike. It is obvious that the first
    strike on the valve stem is the only one which has released air. 
    The first strike on the Valve stem is the only one that depresses the valve stem sufficiently to release air.  The degree of free flight of the hammer is easily adjusted in these FX rifles.
    I hope these inputs are of value in showing how it works and some of the history. … Best regards, Harry.
    Please open the video.
    http://redirect.viglink.com/?format=go&jsonp=vglnk_148724009113614&key=0eff82a158b9bcd735539ea921a97f93&libId=iz87x422010009tm000TA3z071btvqetq&cuid=f-&loc=http%3A%2F%2Fwww.network54.com%2FForum%2F79537%2Fthread%2F1354003980%2FHammer%2Bstrike%2BSM%2Bvideo%2BFX%2BElite%2B—%2BFor%2BChip%2BSmith%2C%2BSteve%2C%2BCO222%2Band%2Bthose%2Binterested%2Bin&v=1&out=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3D4-489J0jzzo%26feature%3Dplcp&title=Airgun%20forum%3A%20Hammer%20strike%20SM%20video%20FX%20Elite%20…%20For%20Chip%20Smith%2C%20Steve%2C%20CO222%20and%20those%20interested%20in&txt=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3D4-489J0jzzo%26amp%3Bfeature%3Dplcp

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