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Thread: Tuning information for HW40/ 75/ P17 owners etc

  1. #1
    Join Date
    Dec 2012
    Location
    Bromsgrove
    Posts
    870

    Tuning information for HW40/ 75/ P17 owners etc

    Recently i have been asked by 1 or 2 club members to look into improving SSP pistols of various types.
    I dont really shoot them prefering springers but i said i would have a look.
    After several weeks of messing around ....machine work....O ring positions etc i think i may have come up with a definative answer for such tuners.
    However i must state from the outset that im not really advocate to recommend such mods to this type of gun but for any interested heres a suprising finding from my considerable experiments..

    Using a stock HW40 and later tuning a 75 i have come to a definate conclusion that the usual piston packing method is not the way to go.
    I produced 0.3mm and 0.2mm spacers to remove volume for the 2 guns respectively with solid coin like disks...before the guns presented zero clearance between the transfer port face bulk head.
    Well actually 0.1mm more than that for each gun but i required a safety margin of 0.1mm before failure to cock and pivot pin strain became an issue.
    Its the later that proves the biggest problem because pivot pin strain will push the entire top strap forward potentially preventing a good tight seal at the breach and thus actually lose power.
    However after hrs of work i have worked out that this is not the answer for another unseen reason.
    These guns do require a bit of clearance volume as part of the flow and pressure maximum.

    The answer is to produce a circular disk like a 20mm dia O ring ( i turned up 0.3mm thick washer disks from Aluminium) then fix these to the end of the piston face.
    These washers act as small volume cylinders at the end of the piston, allowing higher pressure build up without restricting the transfer port clearance required.
    You must make sure the washer has a greater internal diameter than that of the transfer port hole which is not central of course. Provided the washer goes right up to the bulkhead but seals around the transfer port we get a small volume booster.
    I got 30 to 35 fps avg with a number of pellets i had on hand..
    It works.....puts all of this type of gun into the 400 fps+ territory that all these guns struggle to realize ..

  2. #2
    Join Date
    Apr 2002
    Location
    Near Wimbledon, SW London, or Lusaka, Zambia
    Posts
    23,637
    thread revival... Anyone tried this ?

    Will have a play myself later...
    Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.

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