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OK, forget the o-ring... a delrin ring expanded by the pins.. should be tough enough, but still give a bit of braking... but how much friction would one need to make a useful difference.. if we are still talking 500N, then I can't see how the weight could ever exert enough force...
Maybe my transfer port one way valve idea has more mileage after all...
Always looking for any cheap, interesting, knackered "project" guns. But not lathes. I have too many lathes. Thanks, JB.
Lord of the Springs
Maybe the cumulative effect of a brake, a weight and transfer port valve could work, Jon.
Unless someone tries it, we'll never know.
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O ring with delrin band underneath, better friction in the o ring material so less force needed, it would survive, being in a proper groove.Originally Posted by Shed tuner
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yeah, perfect.. if you could please just knock one up and test it, the R&D department is awaiting the results !?
I do enjoy this board
Always looking for any cheap, interesting, knackered "project" guns. But not lathes. I have too many lathes. Thanks, JB.
Registered User
😂 afraid my enthusiasm qouta is nearly used up on this one , straight after the hw95 .
Once the boingerati have tested it's going in the ft gun to see if it's really any better !
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Just as a thought, I added all of the seal compression force to the friction, so effectively a maximum case. Then set it up for a small piston impact to give maximum force (from the impact rather than just chamber pressure). The friction goes off the scale to about 2000N, BUT only for 0.1ms. Power went up from 10.5 to 10.6, piston bounce reduces from 18.7mm to 18.2mm, so probably not ground breaking..
To put into context, simply doubling the pellet friction is worth about a 25% reduction in piston bounce (18.2mm vs 13.3mm), a much softer landing and power goes from 10.5 up to 11.9 ftlbs. (edit - this probably suggests that the port is too big, but you get the idea!)
Lord of the Springs
Doubling the piston seal friction surely, Jamie?
Registered User
No it is pellet friction! In my model the pellet friction is one of the most dominant factors by far (apart from TP diameter). Probably because the transfer port flow equations assume flow based on an orifice plate model. 10N of (constant) piston seal friction is completely negated by an extra few mm of spring compression.
If the release friction for the pellet is too low (~1N) then the pellet will move before any significant pressure has built up in the chamber (or barrel).
For anything around 1 to 10N I can get fairly reaslistic behaviour, but it is effectively controlling the barrel expansion volume (flow is still limited by the TP port).
If the pellet friction is extremely high (~200N), then we have the equivalent of a closed piston and get damped simple harmonic motion of the piston.
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