1. The Forum Rules have undergone some minor changes and updates.  Please take the time to read them; it will only take a couple of minutes of your time. By doing so, you lessen the chance of incurring the wrath of the moderation team or making yourself look foolish to other members.

    90% of users posting adverts in the Sales forums need to be reminded to read the rules as their posts are wrong.  This is unnecessarily time-consuming and will no longer happen - if your advert doesn't follow the Sales Rules it will be deleted and you'll have to start all over again.

    To close this box once you've read it (and the Rules), click on the X in the top right-hand corner.

    Thank you.

    AGF Staff



    Dismiss Notice
  2. A reminder of one of the Forum Rules:

    'Behaviour

    Do not make inappropriate or offensive posts - including threats, harassment, swearing, prejudice, defamation, deliberate insults or name-calling, other negative remarks about this forum, its moderators and administrators or your fellow members. Even if this is just your own personal opinion, RESPECT YOUR FELLOW MEMBERS.'

    There have been changes made to our censoring software in an attempt to help with this growing problem.

    Click the X in the top-right-hand corner to dismiss this notice.
    Dismiss Notice
  3. Dear members,

    Our membership (like our country) consists of people from all walks of life; different in far more ways than can be listed here and each with a different view based on their experience of life - regardless of their colour, religion or cultural heritage. Every single person in the UK has been born of mixed race – we are a multi-coloured and multi-cultural country.

    As many of you are aware there are a handful of individuals amongst this membership that persist in making provocative, inflammatory, racist and otherwise offensive comments. This has been happening across the forum to a certain degree but is most especially prevalent in the Adult section.

    The moderation team has tried to stay on top of this, however unfortunately because of the ‘offensive’ nature of much of its content we don’t monitor the Adult section quite as much as perhaps we should. As a result much of this behaviour has gone unnoticed unless it has been reported to us. While the team always intended to take a "light touch" approach to the Adult section it would seem that some people aren’t quite adult enough to be left unmonitored after all.

    This behaviour is, and always has been against Forum Rules as well as the specific stipulations of the Adults forum and it will no longer be tolerated. We feel it's time to draw a line in the sand and as such from this point onward offenders will receive an immediate and permanent ban from the forum.

    In order for us to achieve our goal of restoring the forum to the friendly and tolerant place it once was, we ask that ALL members be mindful of the content they post and help us to stop unacceptable behaviour by using the 'Report' tool at the bottom of any offending post - the results of which can be seen only by Admin/Moderators.

    You should all receive a copy of this message by PM. 

    To close this message box, click on the 'X' in the top-right-hand corner.

    Dismiss Notice
  4. Hotmail block emails from us entering your inbox. Unless you can setup a safe sender you will not get activation emails from the forum. Please use an alternative provider or complain to Hotmail.
    Hotmail addresses include.

    @Hotmail.co.uk @Hotmail.com @outlook.com @Live.com
    Dismiss Notice
  5. Postings on Politics, Religion & Controversial Off-Topic Material

    The majority of users do not want to read about these subjects and people have left the forum as a result of it – this is after all an 'Airgun' Forum. It’s all very well to say they don’t have to read it if they don't want to, but as most of us use the ‘New Posts’ button there is no easy way to avoid it.

    All AGF staff members are in favour of people being able to discuss what they want, but we have to draw the line somewhere if it is upsetting other users. We don’t want to read about these topics either.

    IMPORTANT- The discussion of politics and religion is no longer allowed anywhere on the forum (including the Adult section).  The only exception is if it's airgun related - they must be put in the Airgun Related Politics section..

    We will not tolerate bullying or personal attacks, racism or any other offensive 'isms'. we will remove these topics from the forum, we will not give you an area where you can abuse each other. We will not hesitate to ban offenders.

    To clear this text box, click on the 'X' in the top right-hand corner.

    Dismiss Notice

Chrono - Cometta 300 and OX spring

Discussion in 'Anything Airgun Related' started by Devondan, Jul 5, 2014.

  1. Devondan

    Devondan Member

    Messages:
    11
    Likes Received:
    0
    Location:
    Devon - funilly enough!
    Hi I'm a new member here, and promise not to post a "what pellet" or "what gun" post (bit like a what oil or tyres on a motoring forum!) ..... Like many I am returning to air rifles from using Meteors and Airsporters in my youth, a Weihrauch HW77 is on my wish list. but for now I have a Cometta 300 that I am using for rabbit control on my land (2 acres). I was offered an ox spring from a friend as you could almost see the pellet drop out of the end of the barrel! anyway I fitted it up (I hadn't seen this post http://www.airgunforum.co.uk/forums/showthread.php/95889-ox-mainspring-in-cometa-300) But to be honest I was quite pleased with the new spring, accuracy and distance was much improved, although cocking was much harder. Anyway being the responsible owner I am I bought a Chrony chronograph and measured what it was doing this afternoon.

    I put 10 Bisley Magnums through first and they came out at 10.5Ft/lbs which I was quite pleased about until I put through 10 Bisley Field, which I mostly use, they came out at 12.76 :confused: I then put 10 Eley Wasps through (the lightest I had) they came out at 13.46 :eek:. I am now stripping the gun down again, and will either chop the spring or get an original item (prob both!).

    But the variance surprised me, I knew pellet weight made a difference but not that much. I understand that if it is ever tested by the police, you don't get to choose the pellets. But how on earth do you make sure that the gun doesn't go over 12ft/lbs? TBH I think the loose fit of the wasps is as as much an issue as the lighter weight, there must be less barrel friction?

    Is this variance normal or due to this spring?

    Dan
     
  2. Jackroadkill

    Jackroadkill Donator

    Messages:
    16,784
    Likes Received:
    114
    Location:
    Drenewydd, Powys, Cymru
    Hi Dan,

    Well, this is quite a common occurrence and it can be very surprising how much variation different pellets can give in terms of muzzle energy. In addition to the weight issue (in a springer, usually a lighter pellet will give a higher reading - but not always, just to cloud the issue - when chrono testing) there's the outside diameter of the pellet to consider as well; a larger pellet may generate more friction inside you barrel and give a lower reading.

    There's not a guaranteed way of making sure that you're under the limit with every type of pellet in every circumstance, but a good rule of thumb is to set power using the lightest pellet you can find (something like RWS Hobbies, for example) and setting the rifle up so that it gives between 10.5 and 11fpe with that pellet. The 12fpe limit is just a limit, not a goal. If you can get the rifle shooting accurately and consistently at 11fpe this will give much more satisfaction (and legality) than a wild and unpredictable rifle that's delivering 11.9fpe.

    Cheers,

    JR
     
  3. Devondan

    Devondan Member

    Messages:
    11
    Likes Received:
    0
    Location:
    Devon - funilly enough!
    Interesting! I'll try and get some lighter pellets on Monday, I'm tempted to get the OEM spring to be honest, there's a Sportsman Gun centre on my work doorstep which is handy!
     
  4. Jackroadkill

    Jackroadkill Donator

    Messages:
    16,784
    Likes Received:
    114
    Location:
    Drenewydd, Powys, Cymru
    I'd infinitely prefer an original spring to an Ox. They do have their supporters but I'm not one!
     
  5. Jackroadkill

    Jackroadkill Donator

    Messages:
    16,784
    Likes Received:
    114
    Location:
    Drenewydd, Powys, Cymru
  6. Devondan

    Devondan Member

    Messages:
    11
    Likes Received:
    0
    Location:
    Devon - funilly enough!
    Fortunately mine looks much better than that!!
     
  7. SteveO

    SteveO Top Poster

    Messages:
    11,080
    Likes Received:
    10,170
    Location:
    Kek
    Dan,

    Not sure what calibre you are using but the lightest pellet I found in .177 was the ThunderBolt at 5.0gr, don't waste your money on these as they don't put out much power!

    I think they are zinc anyway and not lead, The lightest I tried in lead were RWS Hobby's but I found that pellets around the 8.0gr mark made the most power in my springer.
     
  8. Meteor62

    Meteor62 Major Poster

    Messages:
    9,029
    Likes Received:
    1,775
    Location:
    Coventry
    Lop a coil off the ox and see how you get on. I'm not a fan of the ox per se' but I put one in a hw77 and it was the gentlest sedate 77 I had ever fired, it was a smidge under the limit at 11.5 . The Titan I originally fitted managed 10.5 but recoil was harsh. When I had the ox in it it fired nicer than my old venom tuned 77!
     
  9. Devondan

    Devondan Member

    Messages:
    11
    Likes Received:
    0
    Location:
    Devon - funilly enough!
    Thanks for the advice guys, I've ordered a stock spring and new seal from Chambers, but will fiddle with the OX while I'm waiting! One thing I'm not clear on is what to lubricate with what, I assume you keep grease on the seal to a minimum? I was going to polish up the piston too as its a bit rough.

    Sorry should have said its a .22 I'll try the Hobbys.
     
    Last edited: Jul 6, 2014
  10. Meteor62

    Meteor62 Major Poster

    Messages:
    9,029
    Likes Received:
    1,775
    Location:
    Coventry
    People have different opinions on lubricating the seal, most will say a little just behind the seal (where the back of the seal is I don't know where they mean) but for me surely during the cocking stroke the grease will get in front of the seal? This will then cause dieselling. This is why I prefer moly paste or dri slide used on the comp tube walls as opposed to grease which in my opinion is to be used between metals to stop metal against metal and on the spring to stop it twanging.
     
  11. SteveO

    SteveO Top Poster

    Messages:
    11,080
    Likes Received:
    10,170
    Location:
    Kek
    Use moly grease on the spring and to coat the piston - a little goes a long way, don't lather in on... just a artists paintbrush dipped in and smear it on, the spring a little more.

    This stuff is cheap in these quantities - http://www.ebay.co.uk/itm/CARLUBE-M...le_Oils_Lubricants_Fluids&hash=item51b139e0ac

    Use dryslide on the sides of the piston seal only, don't let moly get near it as it will get into the compression chamber and cause dieseling.

    I use the dryslide that is supplied by Welsh Willy in his spring kits, there is some available on eBay in aerosol form but it is prohibitively expensive, anyone else know a cheaper supplier?

    http://www.ebay.co.uk/itm/ROCOL-DRY...583?pt=LH_DefaultDomain_3&hash=item4d1f57f7e7
     
  12. Devondan

    Devondan Member

    Messages:
    11
    Likes Received:
    0
    Location:
    Devon - funilly enough!
    I'm ok for the moly grease - got a big tin! No Dry slide though.
     
  13. Devondan

    Devondan Member

    Messages:
    11
    Likes Received:
    0
    Location:
    Devon - funilly enough!
    Ok got home today to find the spring and seal in the mail box - thanks to Chambers for a quick delivery! Didnt have any dry slide so used moly on the spring and piston and a tiny bit of silicone on the seal. The Cometta spring is longer but has thinner wire than the ox, the ends weren't flattened off very neatly so I sorted that with the side of the bench grinder wheel. Put it all together, no dieseling and the gun fires nice and smoothly, no twang to speak of, the trigger is still a bit heavy but not much I can do about that!

    I need to run some more pellets through it but the good news is that the Wasps are running at 11.6 ftlbs, the Magnums at 8.46 and the Fields at 10.97.

    I have quickly re set up the scope using targets on a piece of 1/2" chipboard, (rain stopped play) the magnums are blowing a hole out the back! Not bad for an old Cometta!

    [​IMG]
     
  14. SteveO

    SteveO Top Poster

    Messages:
    11,080
    Likes Received:
    10,170
    Location:
    Kek
    Sounds good Dan, do try the gun with some RWS Superdomes as I have found they produce the most power. Sometimes it's not all about the weight of the pellet but sometimes the size of the head can also effect the power output. :up:

    Looks like you know what you're doing anyway, good on you for having a go at some DIY! ;)
     
  15. Devondan

    Devondan Member

    Messages:
    11
    Likes Received:
    0
    Location:
    Devon - funilly enough!
    I mostly rebuild engines and race classic motocross, so am happy taking things apart and putting them together again! Great help and advice on this forum. I'll try the super domes as well but those magnums sure carry a kick!
     
  16. SteveO

    SteveO Top Poster

    Messages:
    11,080
    Likes Received:
    10,170
    Location:
    Kek
    We seem to have similar interests, :up: I renovated a knackered old KX80 (pre KIPS) most recently for my son, a total nut and bolt refurbishment... I loved every minute!

    Before and after pic's - fast little thing, even with my ass on it! :D
     
  17. Devondan

    Devondan Member

    Messages:
    11
    Likes Received:
    0
    Location:
    Devon - funilly enough!
    Nice Kwacker! I'm always amazed how quick the little bikes are!

    YZ No 1 (1977) Before: [​IMG]

    After: [​IMG]

    YZ no 2 (1981) [​IMG]
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice