Volume Cylinder Barrel Ratio Measurements

Tech Talk
1

Hey Brainstrust,

Went to replace the noisy spring in my new (used) SLR ION and things got out of control…

Checking that I’ve done these calculations correctly for entry into the calculator

Measured the length of the cylinder with the cylinder head in place, which gave me 66.21mm of usable volume inside the cylinder

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Then measured the overall length of the piston 77.5

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Then calculated how much of the piston would be left outside of the cylinder at its furthest point of travel 62.07, and deducted that from the overall length of the piston which gave me 15.43mm of the piston inside the cylinder

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So… with 66.21mm of usable volume inside the cylinder, taking away the 15.43 that the piston would take up, I have a cylinder volume of 50.78mm to enter in to the calculator.

With a 7.5mm barrel length of 295mm I should end up with a ration of 1.69 : 1

image

Am I on the right track?

2

Not a bad VE ratio at all. :+1: nice work.

Most people just calculate using the overall cylinder length without condidering the cylinder head because the difference is minimal to the IB length.

Technically the swept volume of the cylinder would be the more accurate way to calculate VE, so the distance from the piston head at the point of sector gear release to the piston head fully seated against the cylinder head.

That said, that particular ratio calculator is designed for airsoft and is usually considered a guide only anyway, so doesn’t really matter.

3

Roger that.

I recall @RokSolid said somewhere to make the barrel slightly longer and work (cut) back if required so I might make the barrel 330 ish

Just wanted to check I was on the right path with measurements before committing

4

I measure the swept volume by starting with the piston all the way forward, then if a port is involved drag the piston back until the oring is on the front of the port.

If full cylinder, mark the gearbox where the back of the piston is, then I close the gearbox and spin the gears until the piston releases. Open the box and measure where the back of the piston is to the mark made from starting point.

Hope that makes sense…

I generally go for 1.7:1… though anything 335mm and longer just go a full cylinder.