in airgun world it has a subject on transfer ports

[robert w]

after reading the part 4 of this article ,it got me thinking. air under pressure builds up to a threshold to where the pellet starts movement and keeps building up speed most of the way down the barrel. then i had 1 of those snap how would this work thoughts. if there was a way to design a valve in the port that helt air pressure till a preset pressure opened real fast would it send the pellet out with more speed and even cushion the piston more , thus extending seal and spring life and make an air gun more powerful? its just a thought and now who has any thoughts on this idea. probably never work but a theorie for spring guns. also see im drinkin coffee so my head is in gear this new year morning

[Scotchmo]

When there is a valve used to delay the release of air it then becomes a pre-charged pneumatic (PCP).

[London177]

I understand what you are saying Robert. I am sure it could be done but I wonder how much of an increase in FPS we'd actually see? Perhaps it would be a lot of work for only a little extra gain in performance? I once put a 24mm carb' instead of the standard 16mm on my Honda C90. I got an extra 3 mph, little torque and used loads more fuel!
regards,
Alan 

[robert w]

When there is a valve used to delay the release of air it then becomes a pre-charged pneumatic (PCP).

  i was meaning on a spring gun not 1 with a reserve of air but anyway its just a thought. but the brits are doin a lot of research on air guns

[Scotchmo]

When there is a valve used to delay the release of air it then becomes a pre-charged pneumatic (PCP).

  i was meaning on a spring gun not 1 with a reserve of air but anyway its just a thought. but the brits are doin a lot of research on air guns

robert w,

I understand what you are contemplating. I considered something similar a while back. In field target competition, there are PCP and piston classes. If I encountered a gun that had both a spring/piston powered pump, and a valve, I would classify it as a PCP. Without a clear distinction, there could be too much overlap between the two.

As soon as you put a valve between the pump (piston) and the pellet, you are creating a reserve of air that will be released by the valve. How and when that air is released is secondary. In a piston gun, their should be a clear air path from the compression chamber to the pellet. The pellet acts like the pressure activated "valve" that you are considering. If the pellets are the correct size and weight, they will release at just the right pressure for maximum power.

A single stroke pneumatic might perform the way that you want and would not need the big spring.

[RedFeather]

I'm not so sure the pellet is constantly accelerating.  High speed photos of pellets leaving a springer muzzle do not show expanding gasses such a produced by a pneumatic.  Why 14" or so seems optimum for barrel length in some guns.  And the transfer port is sort of a vortex.  Change the shape and you change the focal point of the max pressure.  Be neat to model it for optimization but I don't think it's doable.   (Fluid dynamics)

[London177]

"Why 14" or so seems optimum for barrel length in some guns"
Remember when barrels were nearly 24" long? I really like the shorter barrels we have today as it makes the rifles lighter.
Someone told me barrels were sometimes kept longer, say 18-20" to keep noise levels down. Any truth in that?
regards,
Alan

[QVTom]

Robert, the pellet is the valve your are thinking of.  We tune it with the leade and radius of the chamber.  Want to delay the release run a tighter leade, larger or harder pellet.  If you go too far the pellet never leaves and the piston just bounces back.  Complex machines springers are

Tom

[Mark 611]

I've done a little transfer port work on airguns {springers} and have opened a few up to a larger dia with some good results, but I'll say this if you go to far you'll rue in the gun! but if you take you time and do it right you can gain about 30 or more fps

[RedFeather]

In fashioning carbines from full length rifles, it seems that some guns actually gain a little speed when the barrel is cropped.  Below about 13" and they start to lose.  Not every gun but some that I've seen reported on.

Fluid dynamics can be counter-intuitive.  Smooth out a surface or entry point and you can actually reduce flow speeds.  Why I, personally, don't mess with transfer ports.  It can often be a case of easy to take off but hard to put back on.

[Scotchmo]

I've done a little transfer port work on airguns {springers} and have opened a few up to a larger dia with some good results, but I'll say this if you go to far you'll rue in the gun! but if you take you time and do it right you can gain about 30 or more fps

Even if you think you went too big, you did not ruin the the rifle. A larger transfer port can make it more pellet sensitive. For a .177, you can go up as much as you want. Well, at least keep it below .165 so the pellet does not fall into the chamber. If you went too big on the transfer port and the shot cycle suffered, there are some remedies. Try a heavier/tighter pellet or if you want to use the lighter pellets, reduce the piston weight.

[Mark 611]

that's not the hole were talking about! what your describing is the leed in for the pellet! the transfer port is the hole in the compression tube where the air is restricted before it gets to the leed in for the pellet,

[Scotchmo]

that's not the hole were talking about! what your describing is the leed in for the pellet! the transfer port is the hole in the compression tube where the air is restricted before it gets to the leed in for the pellet,

I'm not talking about the "leed in".

Once you reach .177 diameter on the transfer port, you are at the maximum that will do any good. And there is now a chance that a dropped pellet will fall through it. So my ports are usually about .160 diameter max.

That said, the tightness of the "leed in" can also affect the firing cycle. So it too becomes part of the mix.

How big did you go when you ruined it?

[Mark 611]

I'm not understanding what your saying here? most transfer ports are between 2.5 and 3.5mm and the average is around 3mm in dia. a .177cal pellet is 4.5mm and a .22cal is 5.5mm in dia, a 3.5mm transfer port is about as big as I've seen on a factory gun, and I would not recomend making it any bigger, but some of the smaller holes can be opened up some and gain velocity. I took a Webley I had that had a 2.75mm transfer port size and the rifle averaged 715fps I opened the transfer port ever so slightly like a half a thousands at a time until I saw no more gain in velocity and ended up gaining 69fps at 784fps with no other changes to the rifle other than port size!

[RedFeather]

While it's cool to hear of success stories like the above, fiddling with ports is not for everyone.  An oversized port is difficult to correct.  Before attempting any work, do a search on the subject.  Tom Gaylord and Jim Maccari both have excellent articles on this.

[Mark 611]

RF I totally agree!

[Scotchmo]

Mark 611,

I don't have any experience with break barrel transfer ports. The transfer ports on Shanghai guns that use the sliding compression chamber (under lever and side lever rifles) are about 4mm even on the .177 caliber rifles. A TX200 uses a 3.7-3.8mm transfer port.

I have not experimented with the smaller transfer ports but I may do so in the future.

[robert w]

looks like 1 could make some threaded plugs to go in the port and then expermint with diffrent sizes and not ruin the gun , mabe brass crewed in from the back side inside the chamber . make several and then increase a size at a time till maxium results are found

[Mark 611]

I see! your talking about sliding compression tubes! well I understand what were talking about now, those holes are as big as they are because they have to cover the barrel and squeeze the breech seal over the leed in, you wouldn't want to open that hole LOL!!! but the transfer port hole in those tubes sit a little deeper behind the the seal area and yes the can be opened up! if you have the know how! If someone has no experience in doing port work I would discourage you form doing so!

[Mark 611]

Robert that's been talked about before and I think someone has done that but I can't remember who!