It is dependant on the diameter as it's the volume that matters. Search the forum for "SCR" or static compression ratio. It's all relative.
Is it the shorter the better, is there an optimum? Diameter not a consideration at this point but let's sat 3,2mm for the moment. Reason for the question is that I am drawing up my own break barrel Air arms seeing as they are dragging their feet!!
Plinkerer and Tinkerer
It is dependant on the diameter as it's the volume that matters. Search the forum for "SCR" or static compression ratio. It's all relative.
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Hi Tinbum, yes I know the scr has to be right but is shortest the best, diameter can be changed to achieve the desired scr. Current design has a 3mm long port but things would be easier if I went to 6/7mm but I don't want to compromise if its better at 3mm.
Plinkerer and Tinkerer
I have experimented , in my tx , with a 21mm diameter comp tube . Down to 4mm long , i have found gains down to 6mm, shorter than that not so much, as i say that's with 21mm dimeter comp tube , will be different at other tube diameters .
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This is the sort of info I was after, I have read that longer ports produce a softer shot cycle but good too long and efficiency is compromised.
Plinkerer and Tinkerer
first question - what kind of shot cycle do you want ? smaller/longer-softer - but obviously that can go too far and lose efficiency quite quickly.
ballpark I'd be looking around the range of 3.5mm x 6mm to 3.0 x 10mm
Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.
I think I will go for 7/8mm. May even look at interchangeable transfer ports for experimenting.
I started drawing it up last year and only picked it up again yesterday. So far have done the breech Jaws and cylinder, breech block and barrel interface. I even bought a second hand TX so I could measure up for swapping parts over. Looking to use the piston, trigger assy and stock.
Plinkerer and Tinkerer