I don't believe a TP smaller than 3.0mm ever works in a 12FP springer....

[Gunfun]

Gasses are indeed regarded as fluids but, being compressible, will behave very differently in a transfer port.

The flow rate link would be spot on if we filled our springer cylinders with water, though.

The more I look at tuning springers, the more mind boggling it becomes.

[trajectory]

When writing my earlier post the idea of filling the cylinder ahead of the piston with water crossed my mind too. I thought if I suggested it someone might say'ok, you first' & I wouldn't fancy trying to dry out intrrnals of a springer, even a clunker of a springer. Still as a theoretical model it would be interesting if the weight of the fluid could somehow be factored out & the empirical perfomance evaluated with changes being introduced step by step so the effects of them could be measured. It would take out any varriability arising from the clmpressability of the air. But how it would translate into the real world is anyones guess so I think the advice that life is too short & its probably better to just roll up your sleeves & get cracking ks good advice.

It will be interesting to see any results from those that have carried them out.......standard rifle v port diameter, differant stroke v port diameter or variability with port volume etc. Its a big topic........but very interesting.

[cringe]

I was thinking about making a brass insert as a transfer port, my idea is to make it tapered down from compression tube, with a convex entry, so no sharp corners, highly polished [mirror]. My theory is based on - as a youth I used to polish cylinder head ports on my motor bikes & it did improve performance - better intake/exhaust flow. just an idea at the moment?

PS. in engineering terms the word fluidic covers both liquid & gas.

[Black Beard]

It is possible to create a model to calculate flow rates. You need to go to modelling all the components, the forces between them and the air itself in the barrel and cylinder. This isn't easy but I did it about 10 years ago. There is no simple formula you can use.

If the transfer port gets too small, the flow between the cylinder and barrel chokes as the air can't go supersonic (based upon its properties in the cylinder). This is a bad thing as the flow levels off and the pressure in the cylinder goes up a lot. The higher pressure air in the cylinder pushes on the front face a lot harder and makes the forward recoil push horrible.

The pressure difference between the barrel and cylinder causes the choking. Smaller diameter ports have more resistance so make the pressure difference higher, which leads to choking. So do longer or rougher transfer ports.

BB

[TonyL]

I was thinking about making a brass insert as a transfer port, my idea is to make it tapered down from compression tube, with a convex entry, so no sharp corners, highly polished [mirror]. My theory is based on - as a youth I used to polish cylinder head ports on my motor bikes & it did improve performance - better intake/exhaust flow. just an idea at the moment?

There has been a number of findings from experiments conducted shared with us over the years and, if I remember correctly, the short answer usually boils down to no fancy shapes / bell mouths etc required. Just a nice, parallel, smooth port with no sharp, jagged edges. I think one of the links that T20 posted onto the thread about HW80 transfer port size to the Pyramydairblog shows a few experiments with differing layouts and I'm sure I've seen plenty of others in the past. That old thread is now on page 1, by the way.. Jim has provided some brilliant information over the years on the subject in Airgun World.

As has been said up above, all very interesting and intriguing stuff.

[cringe]

There has been a number of findings from experiments conducted shared with us over the years and, if I remember correctly, the short answer usually boils down to no fancy shapes / bell mouths etc required. Just a nice, parallel, smooth port with no sharp, jagged edges. I think one of the links that T20 posted onto the thread about HW80 transfer port size to the Pyramydairblog shows a few experiments with differing layouts and I'm sure I've seen plenty of others in the past. That old thread is now on page 1, by the way.. Jim has provided some brilliant information over the years on the subject in Airgun World.

As has been said up above, all very interesting and intriguing stuff.

OK, thank's for that. so it's back to the drawing board for me!