changing xfer port size



Author Topic: changing xfer port size  (Read 387 times)

Offline JimLC

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changing xfer port size
« on: February 27, 2014, 02:26:17 PM »
After reading up on changing the air transfer port size on springers, I've decided to reduce the size of the one on my .177. My (noob) question is, why does no one just braize over the hole...then re-drill it to desired size? I've read of brass sleeves, of set screws drilled out and other methods, but no fill and re-drill? -Jim
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Offline Big Bore Bart

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Re: changing xfer port size
« Reply #1 on: February 27, 2014, 03:03:27 PM »
    You don't want to change the temper of the steel (If it's even been tempered).   Also heating the tube may cause it to warp. :o  One other factor is some steel alloys crack instantly when brazed.
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Offline Motorhead

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Re: changing xfer port size
« Reply #2 on: February 27, 2014, 03:27:48 PM »
Yup, heat to the degree brazing takes will for starters destroy the bluing contrast.  maybe un-bond parts that have sleeve retaining compounds or been silver solder sweat joined.  The temper change is also very real !!
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Offline David.Soliman

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Re: changing xfer port size
« Reply #3 on: February 27, 2014, 03:49:03 PM »
Is there like a swept volume/port diameter ratio???
I read a thread where a fellow experimenting with different port sizes it was on the yellow form IIRC but I don't recall any formulas or anything it was more of a trial and error.

Offline OleTomCat

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Re: changing xfer port size
« Reply #4 on: February 27, 2014, 09:47:57 PM »
Bob Sterne just posted on another thread about changing port sizes, had diminishing returns as it went up...
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Offline JimLC

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Re: changing xfer port size
« Reply #5 on: February 27, 2014, 10:56:43 PM »
Wasn't increasing..was thinking about reducing. From all I've read on the subject, it seems the engineers did a pretty good job on figuring out the right port size to provide the best performance for a variety (to an extent) of pellet weights/types for any given rifle. That being said however, through some experimentation some have found out, that some rifles of the Chinean persuasion, especially .177 did benefit from a reduction in port size on a medium grain pellet. I should have my (poor mans)  chrono put together in a few days and I'll test before and after and post results. - Jim
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Offline Kailua

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Re: changing xfer port size
« Reply #6 on: February 28, 2014, 12:02:50 AM »
Experts correct if I am wrong.  Changing port size has some thing to do with the air volume area added into the equation also.
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Offline OleTomCat

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Re: changing xfer port size
« Reply #7 on: February 28, 2014, 12:25:17 AM »
Experts correct if I am wrong.  Changing port size has some thing to do with the air volume area added into the equation also.

I would venture to guess that making the transfer port smaller allows the pressure to spike higher in the compression chamber before the pellet gets moving...
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Offline Paul68

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Re: changing xfer port size
« Reply #8 on: February 28, 2014, 12:27:14 AM »
Real rough subject to deal with. Honestly, there are easier ways to managed and adjust power levels and performance, like springs sizes, reducing coil count, reducing volume, lightened piston, ect ect. The port sizes appear for most brands to be a compromise to allow good performance across .177 and 22 versions of the same rifles. Some rifles, like the OP mentioned, really can stand some work on the port. My Jet for instance for all its grunt didn't want to fling heavy pellets, when it should have loved 18 to 21 grainers. Turned out the transfer port was tiny compared to magnums of almost identical specifications. Once I drilled it out several sizes larger, lo and behold peak power output did indeed appear with heavier pellets. Overall power didn't change much, only minimal gains, but the gun no longer likes light pellets, and is a much smoother shooter with the heavies. Most guns though, the changes created with a transfer port modification are so small as to be almost unnoticeable, hence not worth the effort.

 

All that hot air aside, I agree. Drilling and tapping is the way to go rather than any filling or brazing. As well as destroying the finish and possibly any soldering/joining that might have been done at the factory, you also need to fill the port ALL THE WAY through, otherwise you could possibly cause all sorts of weirdness with screwed up air flow at the high velocities and pressures that pass through that little port. Which I imagine would be tough to do since you'd have to contend with material protruding into the compression chamber and somehow leveling it within the tube floor before redrilling.



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Offline HYspd

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Re: changing xfer port size
« Reply #9 on: February 28, 2014, 01:26:10 AM »
reducing the coils of a spring is a 2 steps forward and one step back dance...

as you remove coils from a given spring the length gets sorter so the preload is less, but the spring it's self gets stiffer....

the total energy of the installation gets a little lower but the power is expressed more quickly...


every time I see a post where some one has shortened a spring a few coils I cringe a bit...


a more predictable way is to go to a thinner wire...or to a larger diameter spring with the same wire...
« Last Edit: February 28, 2014, 01:29:47 AM by HYspd »
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Offline JimLC

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Re: changing xfer port size
« Reply #10 on: February 28, 2014, 02:37:10 PM »
Good input guys, thanks. I'll post my results when I get done.
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Offline Dockey 454

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Re: changing xfer port size
« Reply #11 on: February 28, 2014, 08:32:55 PM »
One thing about reducing port size, and correct me if I'm wrong. Wouldn't that cause the piston to bounce more with the added back pressure.
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Offline OleTomCat

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Re: changing xfer port size
« Reply #12 on: February 28, 2014, 09:44:34 PM »
One thing about reducing port size, and correct me if I'm wrong. Wouldn't that cause the piston to bounce more with the added back pressure.
  Tom

It would for heavy pellets but In theory for the lower end of the usable range it would work better.
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