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Advice gun power issue.

Discussion in 'Anything Airgun Related' started by Greg1983, Jul 26, 2014.

  1. Greg1983

    Greg1983 Busy Member

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    Hello guys.
    I bought a rifle from new that was firing just over 12ftlb.. I tested it with bisley mags only, these are 21.4\6 grain now I do know that from new a rifle is well greased and lubed up so it can have some dieseling effects on the gun so I decided to send some pellets through the rifle and see how it would test later "keep in mind I never left the house with the rifle"

    Now in the mean time I had only done one alteration with this rifle, it had a plastic barrel end with a fibre optic sight which I removed to fit a silencer adapter to the barrel as the gun had a noisey crack when fired, but after removing this plastic I found the barrel end was machined with different depths and grip thread that gripped the plastic mould..

    [​IMG]

    I then chose to cut this down to the where the barrel is straight "so I removed an inch if that" and recrowned the rifle and fit a silencer adapter + silencer, so now after all that the gun has fired from 500 to 700 pellets through it I decided to test it over the chrombo with bisley magnums 21.4/6 grain, accu pell 14.3 grain & pointer by lanes 12 grain pellets its still firing over 12..

    So I decided to return to the shop and explained my problem with the rifle and the bloke was very understanding and helpful and offered to sort it out but me being me I want to learn my self so I opted for reducing the power my self by clipping a ring or 2 off the spring whilst testing each time I reduce its coils.

    Oh One thing that did bug me though was a fella that they had working in the gun shop "I think he's a gun smith" any how as the shop owner was really helpful this other guy was saying the guns shooting over because the barrel was less than an inch shorter.. And seemed to dismiss the fact that i told them that before i even touched the barrel the gun was shooting just over! Now I'll admit now I ain't no ballistics expert and I could be wrong but doesn't shortening a barrel effect accuracy and reduce or or results in a power loss or range decrease??

    Could this really increase power? What do you guys think?
    [​IMG]

    Thanks in advanced guys and any advice will be appretiated, Greg.
     
  2. Ganton Gunner

    Ganton Gunner Super Duper Moderator Staff Member Mod/Admin

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    longer barrel normally increases the power and shorter normally reduces you are correct
     
  3. Greg1983

    Greg1983 Busy Member

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    Cheers gantongunner, thats what I thought but this fella was telling me otherwise.. Next time I pop in I'm going to ask the chap if he's just a friend of the shop owner and not a gun smith as his knowledge on barrels is incorrect!

    Cheers, Greg.
     
  4. scottroutledge

    scottroutledge Engaging Member

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    Don't forget to heat the spring and flatten then polish the cut end mate. Hope you get it sorted so when we get out up my perm soon you can bring it along with you.
    Scott
     
  5. Greg1983

    Greg1983 Busy Member

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    Yeah bud I'm just getting ready now to pop and buy a torch to heat it up and collapse the cut coil flat, also going to reduce the plastic washer size on the guide rod.. One other idea I'm thinking of is reducing some of its recoil? Is it possible to add some shock absorbing material to the guide rod?

    Cheers, Greg.
     
  6. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Springers are funny things; their reaction to changes in barrel length depends on numerous factors including pellet weight, size and fit, spring rate, piston bore and stroke.. if everything's optimal I'd expect removing a bit of length to reduce energy slightly; although in practice it could make no difference or indeed lead to a slight increase.

    A couple of other things - fair play for wanting to sort it out yourself but tbh it should have gone back to the shop under warranty; something that will be less easy to do now you've lopped the end off the barrel.

    Secondly, removing the end of the barrel can have serious implications for accuracy - a) you've probably removed a choke which could ruin accuracy in it's own right, b) the barrel has to be refinished and recrowned square and properly (in a lathe) - if the muzzle of the gun is sporting a similar rough and wonky hacksaw cut to the pictured part that's been removed, I'd relinquish all hope of hitting anything I'm afraid :eek:
     
  7. terry1001

    terry1001 Major Poster

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    Barrel length changes can have different effects. When you shorten a barrel you remove some of the friction that would have affected the pellet which would tend to increase velocity. There is also less time for the air pressure to act upon the pellet but the effect of this will depend upon several factors relating to the way the air is transferred to the barrel. There is an optimum length (for maximum velocity) for different rifles and, generally speaking, the makers will have designed the gun so that it works reasonably well and has the appearance and proportions that they think will appeal to buyers.
    It is likely that shortening your barrel slightly would reduce velocity - if you had measured the power before/after do you not have velocity measurements to show this?
    I don't normally do any work on spring air rifles but I wouldn't heat up the spring as it will affect the temper and could cause problems, I would grind the cut end flat taking care to keep it as cool as possible. If you are thinking of some modifications to improve the firing cycle you could contact Tinbum who does produce various kits which have received positive reviews from users.
    Although rifles will vary it would be usual for a spring air rifle to develop more power with lighter pellets, pcp guns are the opposite.
     
  8. Greg1983

    Greg1983 Busy Member

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    Testing before and after the barrel cut the gun was more or less the same in power just over 12 and as for the recrown it was my first attempt but wasn't hard to do, took about 2 mins to do with a drill and wet and dry paper.
    [​IMG]

    Gun shoots straight before and straight after, it also passed cotton bud test first time.

    Cheers, Greg.
     
  9. SteveO

    SteveO Top Poster

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    Did you use a wood countersink attachment to do the crown Greg?
     
  10. gtfreight

    gtfreight Not so busy member.

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    If it's just over with Bisley Mags I would think it would be well over with lighter pellets. Try some RWS Hobbys, they are very light, and see what they're putting out.
    I hope you get it sorted.
    Gary.
     
    Last edited: Jul 26, 2014
  11. mattyts

    mattyts Donator

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    As Steve said,what tool did you use to cut the crown? Just because it's smooth and passes the cotton bud test,it dosen't mean it's concentric to the bore.
     
  12. Greg1983

    Greg1983 Busy Member

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    Yeah stevo I posted my method with pictures in another thread, its a quick and simple 2min job.

    Yeah bisley take it just over so I'd imagine lighter pellets would go over higher tbh some pointer and lanes 12 grain would take it further over...

    Wood counter sink, then some wet n dry fine grit to rub with phumb and done.. Shoots straight so its worked well and the chap in the RFD seemed to compliment it so it can't be bad?


    Cheers, Greg.
     
    Last edited: Jul 26, 2014
  13. SteveO

    SteveO Top Poster

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    Only reason I asked was I can see some undulation in the camber of the crown chamfer.... a typical result of using a wooden countersink bit. I use a diamond encrusted Christmas tree bit personally which gives a nice clean and straight chamfer. If it shoots straight, it shoots straight! :up:
     
  14. Greg1983

    Greg1983 Busy Member

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    Hi guys, just thought I'd post an update about the issue I had with my rifles power from new.

    As you may know if you had commented or read the previous comments I had the problem of my new rifle shooting hot :( and instead of returning it I decided to tackle this problem my self "call me stupid but it was a perfect opportunity to Learn something new, which could be handy later on if the same issue happens again?"
    Well to cut a long story short I cropped my spring down a coil or 2, used a torch to heat it up and collapsed a coil and filed it to a smooth flat bottom then rebuilt my rifle and tested it and this is what the results where testing 3 different pellets 10 shots each brand.

    Pointer by lanes .22 / 12 grain weight = 11.8 ftlbs
    Webley accu pell .22 / 14.3 grain weight = 11.6 ftlbs
    Bisley magnums .22 / 21.4 grain weight = 11.3 ftlbs

    I'm thinking these numbers are a touch high still but none of the shots went over the 12! And i think that they may drop once i test it some more as I did clean and grease the gun up before doing this so possible some dieseling effects could be happening? But none the less I'm still well pleased with the results so far considering its been my first time doing a power reduction and to be sub 12 is a relief! :D

    I would like to say a big thanks to the members that shared some tips/knowledge with me! It was useful and very appreciated!

    Cheers, Greg.
     
  15. mattyts

    mattyts Donator

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    Keep an eye on it,it may rise once it beds in.
     
  16. Greg1983

    Greg1983 Busy Member

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    You can count on it! It won't be leaving the house until I'm confident its tamed to a safe limit! If it does creep it will get the snip again :)
    Cheers, Greg.
     

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