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Hammerli AR20FT single reg conversion

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I posted this over on StB hoping for some help bit its been a blow out so I'll try here....

Being a bit of a tinkerer I decided to try converting the reg from its standard double reg set up to a single reg set up as I only ever fill to 200 bar. But Im a little confused as to whats happening over the chrono. Initially from a full charge Im getting 780fps with AA 8.4s but as the cylinder pressure drops the velocity steadily drops as well to 750fps at around 100bar.

Any ideas why its doing that? I cant get my head around whats happening. Theres no creep so the piston is sealing ok but I guess the pressure at which it seals is changing, or am I on the wrong track there?

There does seem to be a slight leak from the cylinder to reg port as when the cylinder is removed after a few minutes the reg will dump its air but with the cylinder fitted its fine, no leaks. Would that cause it?

Ive now shimmed the hammer spring and it seems to have evened out the power curve (slope) but its only doing 760fps average. So I guess the reg spring washer stack needs playing with. Theres no adjustment on the reg so do I shim the stack or add another spring washer? But in what orientation?

Edited by SteveC200

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