Is there such a thing as a 12 fpe Discovery transfer port?

Is there such a thing as a 12 fpe Discovery transfer port?

Joined: October 14th, 2006, 12:30 am

July 5th, 2012, 7:29 pm #1

If so, does anyone know the part#?




Thanks in advance







Vines
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Joined: February 17th, 2010, 3:30 am

July 5th, 2012, 9:16 pm #2

However, this information may give you what you are looking for.... Using 14.3 gr. pellets....

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A 0.070" diameter transfer port operating at 1600 psi gave me 12.1 FPE, and at 1200 psi, it was 11.2 FPE.... With a stock hammer strike, the velocity should also fall off normally above 1600 psi.... I don't have a shot count for you, however, I just did the velocity measurements at three pressures using an otherwise stock Disco (but tethered and fed through the Foster fitting from a regulated tank)....

You can purchase a 0.070" stepped transfer port for a Canadian (under 500 fps) 1377 that fits, but I have no idea of the part number.... You may be able to order it through www.scopesandammo.com .... There were at least two different sizes used, so make sure you give him the size.... Alternately, solder up a Crosman one and redrill it....

Bob
Last edited by rsterne on July 5th, 2012, 9:18 pm, edited 1 time in total.
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Joined: November 17th, 2006, 3:51 am

July 6th, 2012, 12:36 am #3

..the sub 12 foot pound UK version was strangled down. Transfer port or a valve mod?
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Joined: November 28th, 2002, 6:26 pm

July 6th, 2012, 1:09 am #4

However, this information may give you what you are looking for.... Using 14.3 gr. pellets....

[/IMG]

A 0.070" diameter transfer port operating at 1600 psi gave me 12.1 FPE, and at 1200 psi, it was 11.2 FPE.... With a stock hammer strike, the velocity should also fall off normally above 1600 psi.... I don't have a shot count for you, however, I just did the velocity measurements at three pressures using an otherwise stock Disco (but tethered and fed through the Foster fitting from a regulated tank)....

You can purchase a 0.070" stepped transfer port for a Canadian (under 500 fps) 1377 that fits, but I have no idea of the part number.... You may be able to order it through www.scopesandammo.com .... There were at least two different sizes used, so make sure you give him the size.... Alternately, solder up a Crosman one and redrill it....

Bob
How do the ratios of MVs produced by the 0.14" port at 1600psi vs 850psi, compare to the same measurement for the 0.07" port?

Just roughly taking numbers off the graphic, it seems that the latter ratio is significantly larger than the former (like 1.4 vs 1.3), rather than smaller. Has my yardstick sprung a leak, or does this example call into question the notion that strangled ports produce more pressure-independent velocities than free flowing ports do?

Steve
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Joined: February 17th, 2010, 3:30 am

July 6th, 2012, 1:10 am #5

..the sub 12 foot pound UK version was strangled down. Transfer port or a valve mod?
transfer/valve porting, and hammer energy.... My apologies, I was not even aware there was a sub-12FPE version for the UK.... If that is the case, then perhaps someone from the UK could provide the information.... It would certainly be possible to strangle one down that far, the .22 cal Hatsan AT-44 is hogtied all the way down to 7 FPE from 30 FPE for the Canadian market just by restricting the airflow....

Bob
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Joined: April 28th, 2010, 12:23 am

July 6th, 2012, 1:17 am #6

How do the ratios of MVs produced by the 0.14" port at 1600psi vs 850psi, compare to the same measurement for the 0.07" port?

Just roughly taking numbers off the graphic, it seems that the latter ratio is significantly larger than the former (like 1.4 vs 1.3), rather than smaller. Has my yardstick sprung a leak, or does this example call into question the notion that strangled ports produce more pressure-independent velocities than free flowing ports do?

Steve
Last edited by robnewyork on July 6th, 2012, 1:19 am, edited 1 time in total.
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Joined: February 17th, 2010, 3:30 am

July 6th, 2012, 1:19 am #7

How do the ratios of MVs produced by the 0.14" port at 1600psi vs 850psi, compare to the same measurement for the 0.07" port?

Just roughly taking numbers off the graphic, it seems that the latter ratio is significantly larger than the former (like 1.4 vs 1.3), rather than smaller. Has my yardstick sprung a leak, or does this example call into question the notion that strangled ports produce more pressure-independent velocities than free flowing ports do?

Steve
I have is that for a 0.140" transfer port, the velocity at 1600 psi was 827 fps, and at 1200 psi, it was 797 fps, a delta of 30 fps.... For the 0.070" transfer port, the velocity at 1600 psi was 616 fps, and at 1200 psi it was 595 fps, a delta of 21 fps.... That's 9 fps less ES for the smaller port, ie a "flatter" curve.... Taken as a percentage, it's pretty much a wash, 3.6% for the larger port, 3.4% for the smaller one....

Sorry, just realized you asked about 1600 and 850.... (that had such a large ES I didn't bother, I had included that data for those interested in running from an 850 psi regulated tank)

0.140" at 850psi was 737 fps, a delta of 90 fps.... 0.070" at 850 psi was 558 fps, a delta of 58 fps.... That's 32 fps less ES - "flatter" for the small port.... On a percentage basis, the ES would be 10.9% with the larger port, and 9.4% with the smaller port.... showing a definte edge even on a percentage basis....

HTHs....

Bob
Last edited by rsterne on July 6th, 2012, 1:30 am, edited 1 time in total.
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Joined: February 17th, 2010, 3:30 am

July 6th, 2012, 1:22 am #8

fitting a smaller port simply restricts the flow, lowering the velocity and energy at any given pressure....

Bob
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Joined: April 28th, 2010, 12:23 am

July 6th, 2012, 1:37 am #9

I have is that for a 0.140" transfer port, the velocity at 1600 psi was 827 fps, and at 1200 psi, it was 797 fps, a delta of 30 fps.... For the 0.070" transfer port, the velocity at 1600 psi was 616 fps, and at 1200 psi it was 595 fps, a delta of 21 fps.... That's 9 fps less ES for the smaller port, ie a "flatter" curve.... Taken as a percentage, it's pretty much a wash, 3.6% for the larger port, 3.4% for the smaller one....

Sorry, just realized you asked about 1600 and 850.... (that had such a large ES I didn't bother, I had included that data for those interested in running from an 850 psi regulated tank)

0.140" at 850psi was 737 fps, a delta of 90 fps.... 0.070" at 850 psi was 558 fps, a delta of 58 fps.... That's 32 fps less ES - "flatter" for the small port.... On a percentage basis, the ES would be 10.9% with the larger port, and 9.4% with the smaller port.... showing a definte edge even on a percentage basis....

HTHs....

Bob
Last edited by robnewyork on July 6th, 2012, 1:39 am, edited 1 time in total.
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Joined: February 17th, 2010, 3:30 am

July 6th, 2012, 1:44 am #10

at least that has been my experience.... An example of carrying restricted airflow to the extreme is the Hatsan AT-44 where Hatsan change a gun that normally shoots 30 shots at 30 FPE within a 7% ES (fill to 190 bar, refill at 115).... to a gun that shoots 180+ shots at 7 FPE within a 4% ES (fill to 200 bar, refill at 90).... Six times the shots with about half the ES on a percentage basis, plus able to use a wider fill range....

Bob
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