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Mk4 Airsporter Preload

Discussion in 'Technical' started by Cinimod, Aug 16, 2021.

  1. paj

    paj Busy Member

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    This is my advice based on my experience, get as close to an original spec spring as possible, Protek did a "standard" AS spring for around £10 or £15 which I have put straight in with original guide and slip washer on piston end, spring smeared with moly grease and just a slight touch on o-ring (Meteor size) and, after several combustion shots and a couple of hundred more, it settled down to a pretty steady 9.5 ft lb ish. Which I was happy with. IMHO then is the time to start with fitting a better spring guide, trimming the spring to allow for a top hat, etc., if you want to fine tune it. Also make sure new o-ring not damaged or too tight but these also need some shots to wear in.
     
  2. Sgibbar

    Sgibbar Engaging Member

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    Do you have a full size piston o ring? Maybe worth trying, the skinny meteor one might not be touching the sides?
     
    Cinimod likes this.
  3. Cinimod

    Cinimod Keyboard Hero

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    No, I got shot of it as it had a whacking great nick in it. Might order one from chambers or try and source a selection of O rings..............dom
     
  4. ricardolamos

    ricardolamos Engaging Member

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    I recently fitted a Tinbum kit to my Mercury which I think has the same sized compression tube as the Airsporter and there was quite a lot of pre-load which necessitated a spring compressor.
    The gun is shooting a very consistent 11.3 ft.lbs.
     
    Cinimod likes this.
  5. Cinimod

    Cinimod Keyboard Hero

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    I’ve got a set of @shauny guides in mine which meant I had to trim the spring to stop it being coil bound. The Mercury also doesn’t suffer from the loss of swept volume that the airsporter does…..dom
     
  6. ajohn

    ajohn Chewing Things Over

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    I suspect it was you that suggested I fitted the same spring to my Airsporter. ;) I have the spring but haven't done anything with them. Need to make a box like item to use on my spring compressor. Mine is an S giving ~8 from memory as it came. Might have been @ped suggestion, not sure.

    They are ~257mm long, 20.6 dia with 3.34 dia wire - as close as I can measure.

    They are also available here but suspect it could well be a different spring going on the models listed but if a lower diameter it could use thinner wire.
    https://www.airgunspares.com/gunspa...irsporter-s/160672bsaasmercurymainspring.html

    It's seems that when people cut Titan etc they work out the compressed length and the solid length and cut for 10% short of fully compressed and then cut to suite. Till power drops is usually mentioned. I've part rebuilt a different gun and after some thought fitted it's stanard spring mainly because I thought it was a good idea to check accuracy first. Much cheaper option than buying a Titan especially as one of 2 could be used. Turns out that one of those would be over powered.
     
  7. Cinimod

    Cinimod Keyboard Hero

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    Right gents, how much difference in power can attributed to pelllet size. Well I'll tell you in a moment.
    I started off be checking to see if the Meteor O ring was too small, well all ok for that part with a nice sliding push within the cylinder.
    Took out the piston sleeve to see if that was binding (as Shauny said it was a bit tight,but would wear in), that put it up to about 420-425. It'll probably go back in at a later date.
    Well, time for the pellets. I've been running it in at the moment with FTT as I had them for my other guns so I wondered if a sample pack of Wasp 5.6 would make a blind bit of difference. Probably not a lot I thought, well you can guess my surprise when it went straight up to 525+ :) but will settle down a bit after the oils burnt off a bit, did the figures and it comes out to a much more healthy 9 ft lbs
    Is 100fps difference a lot or is it just me that thinks it's is.

    I am slightly more optimistic now that it'll work out fine in the end. The only thing I did notice was that as it was dieselling to start off with it has showed up a puff of white smoke from the rh side of the tap which I can live with...........dom
     
    Sgibbar likes this.
  8. landymick

    landymick Big Poster

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    I’ve used Vulcan springs that work ok .
     
    Cinimod likes this.
  9. Cinimod

    Cinimod Keyboard Hero

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    I'm not too clued up on the playing with different springs so that's why I went with the standard Airsporter one from chambers. I'm not too concerned with huge power I just want a nice smooth to shot gun...........dom
     
  10. landymick

    landymick Big Poster

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    I used a slightly smaller o ring as well , much better . I used the original base washers & added 1 x 2mm delrin washer in the piston .
    Simple clean & polish & re lube with moly .
     
    Cinimod likes this.
  11. SlugFest

    SlugFest Posting Addict

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    Sounds to me like you're overcoming some hurdles Dom :thumb: It's going to be very worthwhile ;)
     
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  12. Cinimod

    Cinimod Keyboard Hero

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    I hope so Jason, I was a bit disappointed with the first set of figures but they seem to be going the right way now...........dom
     
    SlugFest likes this.
  13. Sgibbar

    Sgibbar Engaging Member

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    I have some Defiant Vintage slugs and some old .22 wasps if you want to try some to see if that makes any difference?
     
    SlugFest likes this.
  14. paj

    paj Busy Member

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    Would expect the power to increase a little as it beds in, rather than drop.
     
    Cinimod likes this.
  15. Cinimod

    Cinimod Keyboard Hero

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    That would be fabs thanks Si :thumb:, I'll bring it along to Taunton on Saturday. I think the only true 5.6 that you can get now are Marskman as the Defiants aren't made anymore and the newer Wasps are supposed to be rubbish, not like the older ones........dom
     
  16. Cinimod

    Cinimod Keyboard Hero

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    That's a bonus then :thumb:.......dom
     
  17. welshwilly

    welshwilly Engaging Member

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    Hi Cinimod. if its a .22 cal give it 24 coils with a Titan spring, take off 1 x slip washer from the rear but keep one there poss 4mm, take out any metal washers from the front, use Top hat and 1 x 3mm slip washer. Use RWS SuperDomes as these are the most consistent pellets I have found for the British Tap Loaders Inc Mercurys.

    When pushing piston home make sure you dont pinch the O ring on the cocking slot.

    WW :)
     
    Cinimod, SlugFest, paj and 1 other person like this.
  18. ajohn

    ajohn Chewing Things Over

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    I came across a 1957 review but no pellet weights available
    1957date1.png

    These cost way more than USA guns at the time - according to the write up anyway as they need to last longer :rolleyes:
     
    SlugFest likes this.
  19. paj

    paj Busy Member

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    Very interesting ajohn. So assuming they must mean No. 2 Bore, that should be close to the expected velocity of a Mk I Airsporter with the true Eley (IMI) 5.56mm pellets. Possibly very similar with the Webley Mk III also? What do you think?
     
  20. Cinimod

    Cinimod Keyboard Hero

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    Evening Will,
    That's a big difference in coils though, the Chambers one has been trimmed down to 31 and that gives a couple inches of preload. Does the Titan one have wider spaces between the coils to give the same spring length? Also I'd need to have another set of guides done. :(
    I know there's differences between springs with regards to how comfortable they are to shot is the Titan one softer?.............dom
     

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