SpudFiles

i am almost finish my co-axial rifle
the barrel is 10mm (outside) and a 8 mm bore, the chamber is 3/4" steel pipe he had 2cm diameter inside.
how much the piston must open far away from the barrel when release the air?

looks like it will be fine but your piston doesnt need to move that much but how long is your piston?

For a barrel with an I.D. of 8mm I would suggest 2 millimeters.

Mr.Sandman wrote:looks like it will be fine but your piston doesnt need to move that much but how long is your piston?

i have to build it soon ,i think about 1 to 1.5 cm
and i think about 1 cm gap

They say that a good rule of thumb is to have the piston travel be at around 1/4 of the barrel diameter... I usualy go with a tad more, just to be safe.

markfh11q wrote:For a barrel with an I.D. of 8mm I would suggest 2 millimeters.

I agree. However, just in case, you might want to bump it up to 3mm, to make sure you are not choking flow.

thank you fellas that's will help me a lot
just in case what if i make the gap 1 cm instead 2 mm ??

far_cry wrote:just in case what if i make the gap 1 cm instead 2 mm ??

More flow, but 1 cm is way overkill and all it will do is add to your pilot volume, therefor reducing overall performance. Do what Mark and Velocity said and aim for 2-3 mm.

You will ALSO be exspanding the air in your chamber making the gun less powerful. Once the piston opens past 1/4 the barrel i.d. then you are just exspanding air into the extra area but it wouldn't make much of a difference.

roger comrades

>>Some thoughts on the subject<<

personally i would aim for 5mm

I think 5mm too

ok i will try thanks