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My HW77 in .177 a brief tuning guide

Discussion in 'Anything Airgun Related' started by larryking28, Jun 18, 2014.

  1. larryking28

    larryking28 Busy Member

    Likes Received:
    Right without wishing to seem I am teaching people to suck eggs I am going to post my findings from messing with my HW77 over the last few days.
    The rifle is a 1988-1989 one so has the 25mm piston that is considered the better tuning choice than the newer 26mm ones,exactly why I wont go into here right now.
    When I first got the rifle I choroned it at about 11.6ft/lbs with 8.4g AAs
    The rifle seemed quite smooth to cock and fire but there was a pronounced twang/reverberation that could be felt through the stock.
    I decided to strip it down and see what was what.
    It looked like someone has been inside it before me as the usual HW grease wasn't present.
    I replaced the breech seal,piston seal and polished the piston,compression chamber (inside and out) and inside the main body of the rifle itself.
    I also cut a couple of coils off the spring.
    I re-assembled it with some LT2 grease and no preload or top hat etc.
    To my surprise it jumped up to the point where it was now technically illegal despite the fact I had shortened the spring although the twang/reverberation had gone.
    I took it apart again and lopped another couple of coils off the spring,power wise it now dropped to just over 7ft/lbs,opps
    To me it just goes to show how much these rifles can be improved upon with just a simple bit of wet and dry and elbow grease.
    I also ordered a Tinbum tuning kit at this point although I wasn't sure it was needed as the rifle was already smooth although that might have been to the low power it was now putting out.
    Anyway the Tinbum kit arrived this morning so I set to work again.
    I put the top hat in the piston along with the spacer for it and one of the spacers on the rear spring guide and reassembled it.
    When I put it back together there was still no real obvious tension in the spring and I could easily screw the end block on by hand.
    The cocking stroke was as smooth as before (maybe a fraction better) and now it shoots at roughly 760fps with only a variation of about 10fps over 10 shots,that works out at roughly 11ft/lbs,success!
    The morals of this story?

    1.Buy a chrono,without it I wouldn't have had a clue what was going on and if I was legal or not.
    2.Don't be afraid to have a go.
    3.I was surprised how about 3-6mm worth of spacers can alter the power from 7ft/lbs to 11ft/lbs
    4.Simple tuning can work,I have no doubt V-Mach etc are good and they give you a full kit but other than £5 for some grease and £20 for the Tinbum kit along with £13 worth of seals I now have a pretty sweet and consistent rifle.
    5.To me the Tinbum kit seems work well and I have consistency that wasn't there with the stock parts even when they were cleaned,regreased and polished

    When I get my HW97 blue laminate stock I will be even happier.
    Get the tools out and have a go people :)
    Last edited: Jun 18, 2014
  2. Jackroadkill

    Jackroadkill Donator

    Likes Received:
    Drenewydd, Powys, Cymru
    Good to see another member who's taken the plunge and then found out that it's not really a plunge at all, it's really easy and very satisfying.

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