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PostPosted: Wed Apr 01, 2015 10:42 pm 
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Joined: Wed Nov 27, 2013 12:54 pm
Posts: 518
I just finished my at44 .22 caliber barrel change from a 19" oem to a lothar Walter 23" barrel.
Great service by Sniper Dan by the way.

I would have tought it would give a few fps more due to the longer barrel without me having to tune anything else than switching to a longer barrel.

Nope nothing ... same exact speed.
Barrel is well anchored and inligned with the tp.
Everything is properly done.
Current rifle setup:
I even got the 5holes plugged and opened the sixtg hole way before changing this new barrel.
Hammer spring preload to minimum (0 turn)
Tube regulated to 100 bar (1450 psi) Altaros regulator
Not sure if the plenum on the regulator. About 25cc maybe

865 fps with jsb 14.35gr.
What do guys think.r
Barrel free floating
White delrin seat opened to about .185
180 cc air reservoir
865 fps with jsb 14.35gr for 55 regulated shots.

Is this normal?
Should I do something else.
I tought a longer barrel was giving me "free speed" .
Does increasing the hammer preload will help without reducing shot count. I already had a good effeciency with the oem hatsan barrel.

The accuracy is not an issue, both barrel gives very good grouping at 50 & 70 yards.

Thank you for any input

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Hatsan At44 Tactical .22
Steyr hunting 5 automatic
Ruger air magnum .22
Weirhauch HW100 .22
Gamo Expomatic .177
Benjamin Marauder DougP custom stock
Theoben SlR98 .22
AlEx Custom gun .22 (JezX built masterpiece) :)
Hatsan Atp2


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PostPosted: Thu Apr 02, 2015 6:30 am 
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Joined: Sun Jan 09, 2011 8:07 am
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Location: Central West River Nova Scotia
IMHO 55 shots at 865 is perfect.

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If I had only one wish, it would be to be able to "unsay" things.


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PostPosted: Thu Apr 02, 2015 6:54 am 
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Joined: Thu Sep 11, 2014 10:59 am
Posts: 482
Location: West of Ottawa
Hi Alexis,
Recently Joe Hickey started a thread called "pressure at the muzzle" and Rsterne posted a graph showing pressure and Fps versus barrel length at various starting pressures. Very cool graph.
The pressure curve is an exponential decay and near the end of a longish barrel, the difference in pressure may be very small between 18" and say 22" depending on how well tuned the gun is. If the gun is wasting air there will be a higher differential between those lengths and a larger difference in Fps.
Since there's not much difference, I'd think your rifle is tuned pretty well. Probably similar to the Orange curve in the graph. (Hope Bob doesn't mind me reposting his picture.)

http://s378.photobucket.com/user/rstern ... s.jpg.html

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- Doug
.................
QB79 .177 (PCP) X 2


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PostPosted: Thu Apr 02, 2015 7:52 am 
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I lost some speed switching from to a LW barrel of the same length in my daisy 953. My guess is that the choke on the LW barrel increases friction and costs a few fps. In your case you may have gained a little from the length and lost a little on a tighter bore. Still sounds like it's working great :)

Jim


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PostPosted: Thu Apr 02, 2015 8:46 am 
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Location: West of Ottawa
Jim's probably right. My interpretation of the graph was over simplified.

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QB79 .177 (PCP) X 2


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PostPosted: Thu Apr 02, 2015 8:57 am 
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Hey Doug, I think your point about the graph and barrel length is right, I was just throwing in another observation to confuse the issue :oops:

I find the graph a bit difficult to interpret, but if I'm reading it right, all the fps lines look pretty flat between 18 and 24" - definitely into diminishing returns for the particular setup being modelled. So yup, it looks like you were right to me.

Jim


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PostPosted: Thu Apr 02, 2015 10:15 am 
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Location: West of Ottawa
Hi Jim,
Where I was wrong is that I was equating pressure directly to velocity. And really a change in velocity would only occur if the forces are unbalanced in front and behind the pellet. So even if there is no difference in pressure between the lengths of barrels there may still be acceleration of the pellet if the force behind the pellet is greater than the force caused by friction.
However, when you look at the graph and see the velocity curve leveling out at that length, it would mean that the forces are equaling out as well. So to get acceleration over the last couple of inches of the barrel, there'd need to be more pressure behind the pellet. You wouldn't need to change the shape of the pressure curve - just raise it up a bit. As you can see fairly easily on the FPE curves - the ones that have the most slope (still accelerating) are the ones that are shifted up on the pressure axis.

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.................
QB79 .177 (PCP) X 2


Last edited by DougP on Thu Apr 02, 2015 10:47 am, edited 1 time in total.

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PostPosted: Thu Apr 02, 2015 10:45 am 
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Joined: Wed Jul 16, 2014 1:24 pm
Posts: 799
Location: Vancouver, BC
joe hickey wrote:
IMHO 55 shots at 865 is perfect.


X2. That's beautiful.

Do you find much of an accuracy gain with the LW barrel? I find my Hammerli Pneuma very pleasing in accuracy with 18gr JSBs. It's no match grade rifle, but I challenged my decision to go with an LW barrel when I realized that I'd have to improve significantly to make it useful.

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Mike

FX Streamline .22 - Optisan Mamba Lite 4-16X44
Hammerli Pneuma Elite 10 .22 - Bushnell Elite 4200 4-12X40
Custom Crosman 2240 w/ LW barrel - Vortex Strikefire
Remington AirMaster 77 PAL rated - CenterPoint 3-9X40


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PostPosted: Mon May 04, 2015 12:29 pm 
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Joined: Wed Nov 27, 2013 12:54 pm
Posts: 518
Well here is an update on the tuning after the barrel swap from a oem hatsan to a LW barrel from the Dan at the caf store.

The accuracy has improved by a few point looking at my paper targets.
I was loosing velocity at first with no hammer spring preload. I turn out 1.5 turn to the preload adjuster.

The gain was significant. I am now using the extra air from the valve in good harmony with the 4`` longer barrel.
I lost about 7-8 shots but gained 90 fps (2 fpe)

_________________
Hatsan At44 Tactical .22
Steyr hunting 5 automatic
Ruger air magnum .22
Weirhauch HW100 .22
Gamo Expomatic .177
Benjamin Marauder DougP custom stock
Theoben SlR98 .22
AlEx Custom gun .22 (JezX built masterpiece) :)
Hatsan Atp2


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PostPosted: Mon May 04, 2015 1:16 pm 
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Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8979
Location: Coalmont BC
If you tune for the same shot count (air use), you should gain in velocity.... The more efficient the tune (with the shorter barrel) the less you will gain.... I would expect to gain about 5% in velocity (10% in FPE) even in a pretty efficient PCP going from a 19" barrel to a 23" without changing the tune at all.... When you are pushing the FPE limit of the gun, the gains can be even more....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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