Seal size confirmation...S400 breech

Discussion in 'Air Arms' started by Knockedover, Dec 29, 2015.

  1. Knockedover

    Knockedover CSFTA Champ

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    I'm looking for confirmation on the size of a .177 S400 breech seal, ive seen two different sizes, bs008 and 4.5x1.5, which is correct? Looking to stick some on an order of o-rings and just want to make sure I get the right ones :)
    Cheers :)
     
  2. DEAN C.

    DEAN C. Steyr Convert

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    I was told these were modified to the thicker MPR size now, so that's why you come up with two different seals.
    I presume that the BS008 will be the MPR and later type, as that is 1.78mm width, but looking at the HFT500 with the the same barrel as the MPR, it quotes using a FP121 (4.5x1.5) so I am confused as well.
    I will try and measure them up tonight as I have both types in stock, the early barrel seal which also fits the gauge bolt, and the MPR/HFT500 later seal FP121, now quoted for all 400's.
     
    Last edited: Dec 29, 2015
  3. Knockedover

    Knockedover CSFTA Champ

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    Cheers :) much appreciated :)
     
  4. cloverleaf

    cloverleaf Active Member

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    FWIW the BS008 / S536 is the earlier, fatter O-ring, replaced by the MPR-spec 4.5x1.5mm / FP121 on later guns.

    My records suggest the O-ring changed between serials 080000 and 115000, however it appears that this change probably occurred when AA switched from two-piece to single piece breech seal carriers - which were introduced around serial 100000 (I'd guess when the F-suffix rifles were released) ;)
     
  5. Tench

    Tench WHFTA World Champion 2016.

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    I keep the bs008 instock as that is the size on the bsa fill probe and it is not the size used in the .177 400 breech. the 4.5x1.5 is the one you need.
     
  6. cloverleaf

    cloverleaf Active Member

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    As above I think you'll find that it varies with age:

    An earlier (Iss 12) S400 manual lists part no. S536 as ".177 barrel seal" on pages 13 and 14. According to Julian's site, part no. S536 is described as "BS008 O RING 70 SHURE".

    Conversely a manual for the current f-suffix guns lists part no. FP121 as "Barrel seal - .177 (4.5mm)" on pages 14 and 15. Julian's site lists FP121 as "4.5 X 1.5 NBR 70 O RING (.177 BREACH SEAL)"

    :)
     
  7. Knockedover

    Knockedover CSFTA Champ

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    Ended up getting a handful of both sizes, as it turned out it was the 4.5x1.5 that was needed however the one that was fitted was a different size that was neither the the 4.5x1.5 or the BS008 so quite what size that was is anyone's guess :D
     
  8. stryder5

    stryder5 New Member

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    Shore hardness shurley.......lol
     
  9. cloverleaf

    cloverleaf Active Member

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    Good work - evidently yours is a later gun (or retro-fitted with a later seal holder) then. Your guess is as goods as mine regarding what came out :p


    Cut and pasted - wasn't feeling pretentious enough to ad [sic] :p
     

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