Transfer port restrictions

Transfer port restrictions

Joined: November 17th, 2006, 3:51 am

June 26th, 2012, 1:31 am #1

Restrictive transfer port.

OK..here is the data. Same gun, same valve, same everything EXCEPT striker springs were swapped. As striker energy increased, the sweet spot pressure also increased.

But the shot count stayed the same.

Spring #1
135 90BAR
10 shots from 620 590fps = 605fps averqage / 11 foot pounds

Spring #2
145- 100BAR
10 shots from 650 620fps = 645fps average / 12.5 foot pounds

Spring #3
165 110BAR
10 shots from 675- 645fps = 660fps.average / 13 foot pounds

SO, If I want a 12 foot pound gun....would running at the higer pressure level and restgricting the transfer port (so that the energy level was at 12 foot pounds) increase the shot count...or not?
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Joined: February 17th, 2010, 3:30 am

June 26th, 2012, 3:07 am #2

in the string at the highest pressure (55 bar instead of 45) and since the string should be slightly flatter if you restrict the transfer port a bit.... you might pick up a shot or two.... I wouldn't expect more than that....

Bob
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Joined: November 28th, 2002, 6:26 pm

June 26th, 2012, 4:38 am #3

Restrictive transfer port.

OK..here is the data. Same gun, same valve, same everything EXCEPT striker springs were swapped. As striker energy increased, the sweet spot pressure also increased.

But the shot count stayed the same.

Spring #1
135 90BAR
10 shots from 620 590fps = 605fps averqage / 11 foot pounds

Spring #2
145- 100BAR
10 shots from 650 620fps = 645fps average / 12.5 foot pounds

Spring #3
165 110BAR
10 shots from 675- 645fps = 660fps.average / 13 foot pounds

SO, If I want a 12 foot pound gun....would running at the higer pressure level and restgricting the transfer port (so that the energy level was at 12 foot pounds) increase the shot count...or not?
...combined with a restricted TP should give more shots at 12fpe - especially if the striker is undebounced in both cases, since a restrictive TP helps limit bounce-related air loss.

Steve
Last edited by pneuguy on June 26th, 2012, 4:48 am, edited 1 time in total.
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Joined: March 1st, 2002, 12:22 am

June 26th, 2012, 5:27 am #4

Restrictive transfer port.

OK..here is the data. Same gun, same valve, same everything EXCEPT striker springs were swapped. As striker energy increased, the sweet spot pressure also increased.

But the shot count stayed the same.

Spring #1
135 90BAR
10 shots from 620 590fps = 605fps averqage / 11 foot pounds

Spring #2
145- 100BAR
10 shots from 650 620fps = 645fps average / 12.5 foot pounds

Spring #3
165 110BAR
10 shots from 675- 645fps = 660fps.average / 13 foot pounds

SO, If I want a 12 foot pound gun....would running at the higer pressure level and restgricting the transfer port (so that the energy level was at 12 foot pounds) increase the shot count...or not?
cuz im thinking thats why im getting the numbers Im seeing

 


dr_subsonic's pneumatic research lab

the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
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Joined: November 17th, 2006, 3:51 am

June 26th, 2012, 11:06 am #5

...on other guns, a reduced transfer port did get the energy to the goal level and did extend shot count. Was pretty close to the total energy with the wide open transfer port.

If it were 10 shots X 15 foot pounds (150) then it worked out to something close to 15 shots X 10 foot pounds (or 20 shots at 7.5 foot pounds).

So for the above gun, are right...would proably pick up one or two shots at best.

(Tiny air volume of abo0ut 44cc's..so there isn't a lot of air to play with.)
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Joined: March 1st, 2002, 12:22 am

June 26th, 2012, 7:27 pm #6

Restrictive transfer port.

OK..here is the data. Same gun, same valve, same everything EXCEPT striker springs were swapped. As striker energy increased, the sweet spot pressure also increased.

But the shot count stayed the same.

Spring #1
135 90BAR
10 shots from 620 590fps = 605fps averqage / 11 foot pounds

Spring #2
145- 100BAR
10 shots from 650 620fps = 645fps average / 12.5 foot pounds

Spring #3
165 110BAR
10 shots from 675- 645fps = 660fps.average / 13 foot pounds

SO, If I want a 12 foot pound gun....would running at the higer pressure level and restgricting the transfer port (so that the energy level was at 12 foot pounds) increase the shot count...or not?
"The TP size gives you the max speed limit allowable by maxed tune settings just like it's bigger brother the Mrod. You should figure what speed your looking for and pick a transfer port size JUST big enough to allow it without having to max out the HS and stroke adjustments."

I think we can all agree that maybe the TP, at .101, is too wide open and does need to be reduced.

If a stock TP is .081, then where to start for a bigger than stock, less than the black hole currently installed? Split the difference and go to .091 from stock? or work up to it, say .085, then .091, then .095?  (This is where we need the externally adjsutable iris TP <img alt="happy.gif" src="/images/happy.gif" width="14" height="14"> )

The other Q I'd have is where to set/start your Stroke and striker preload adjustments... in the middle and work them forwards or back as you get numbers?

I think what I'm gonna come away with from this exercise is a huge reinforcment of the concept of a "shooting system".

 


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the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic
Last edited by dan_house on June 26th, 2012, 7:33 pm, edited 1 time in total.
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Joined: November 17th, 2006, 3:51 am

June 26th, 2012, 9:17 pm #7

Really not a whole lot of difference in some ways. Valve just "knows" how hard its been smacked. Can get to the same energy output with a stiff spring and a short stroke as you can with a weaker spring and a longer stroke.

Its a complication I prefer to leave to the end of the tune...often just set it at mid point and then use it to dial into the energy wanted once I get close with the other adjustments.

Of course, if looking for the max possible energy, make the stroke as long as possible.

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Joined: March 1st, 2002, 12:22 am

June 26th, 2012, 9:23 pm #8


getting the shot curve to flatten out, I'm finding a tad more diificult

But thanx for saying what I was thinking, start in the middle and tweak from there....




dr_subsonic's pneumatic research lab

the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic
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Joined: November 17th, 2006, 3:51 am

June 27th, 2012, 12:52 am #9

...on other guns, a reduced transfer port did get the energy to the goal level and did extend shot count. Was pretty close to the total energy with the wide open transfer port.

If it were 10 shots X 15 foot pounds (150) then it worked out to something close to 15 shots X 10 foot pounds (or 20 shots at 7.5 foot pounds).

So for the above gun, are right...would proably pick up one or two shots at best.

(Tiny air volume of abo0ut 44cc's..so there isn't a lot of air to play with.)
Transfer port results...just one test.

This carbine started out as a 12gr....then went to bulk fill...then to co2 tanker....then to HPA...and then to HiPac PCP. Because of this co2 origin, the transfer port holes in the valve and the barrel have been reamed out to extra large size (like .125).

The first tests had a transfer port tube of .150...which didn't really help over the .125 restrictions of the valve and the barrel. Figure the 2250 HiPac tube runs something close to 44-46cc's

The original wide open transfer port:
2400-1550psi
629
639
642
647
650
654
653
650
649
642
638
629
631
621

Which could be read as:
25fps = 12 shots
3% = 10 shots

Average: 641fps/13.5gr./12.3fpe+
Efficiency: 15.3 bar/cc


Transfer port changed to one .088. No other changes.
531
542
545
552
556
558
562
566
560
561
560
561
570
570
567
564
560
555
548
545

25fps = 18 shots
3% = 14 shots

Average: 556fps/13.5gr./9.3 fpe+
Efficiency: 14.2 bar/cc

So if you look at it from energy delivered (inside of 3% velocity variation):

large port: 12.3X 10 = 123 foot pounds
smaller port: 9.3 X 14 = 130 foot pounds

If you look at it as shots inside of 25fps:

large port: 12.3X 12 = 148
smaller port: 9.3 X 18 = 167

So..evidently a reduced transfer port does a little bit more than redistribute the same energy over a longer number of shots...it evidently does add a bit of efficiency. Will work on getting the efficiency up...doubt it will make more than 1 or 2 shots per fill difference (and that probably equal amount the two tests).
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Joined: November 17th, 2006, 3:51 am

June 28th, 2012, 1:58 am #10

Restrictive transfer port.

OK..here is the data. Same gun, same valve, same everything EXCEPT striker springs were swapped. As striker energy increased, the sweet spot pressure also increased.

But the shot count stayed the same.

Spring #1
135 90BAR
10 shots from 620 590fps = 605fps averqage / 11 foot pounds

Spring #2
145- 100BAR
10 shots from 650 620fps = 645fps average / 12.5 foot pounds

Spring #3
165 110BAR
10 shots from 675- 645fps = 660fps.average / 13 foot pounds

SO, If I want a 12 foot pound gun....would running at the higer pressure level and restgricting the transfer port (so that the energy level was at 12 foot pounds) increase the shot count...or not?
OK...with a goal of 12 foot pounds and a tiny air volume of an estimated 44ccs, kept playing with the transfer port. Striker hit was running the carbine at 160-110BAR (or about 2350 to 1600psi.

Changed the tension UP a little bit (one pre
tension turn of the screw), swapped for a striker that was 10gr. Lighter, and changed the transfer port to .072 ( 5/64ths).
[IMGhttp://i157.photobucket.com/albums/t50/ribbonstone/Hip Ac/DSCF1899.jpg[/IMG]

14.3gr. Benjamin Cylindrical

581
597
601

606
613
620
623
628
628
625
624
618
614
606
608
607
610

596
597
579

Which works out to:
25 feet per second = 628 603= 14 shots

So... 2350-1600 fps...44cc....20 shots...601fps average...call it a BAR/CC-FPE of about 10.

Just saying.

Is not a great long shot count, but it has a dinky air volume.
Efficiency of 10 is pretty good for a 12 foot pound gun (OK..call it 11.5 to 12.5 gun).

Suggestions:

1. Restrictive transferor port is USELESS if looking for maximum velocity.
2. The increase in shot count with a strangled down transfer port is VERY CLOSE to the same energy x shot count of a wide open transfer port...it just doles out the energy over a long time frame.


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