GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: dyotat100 on March 14, 2014, 09:53:56 PM
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I was asked to start a topic on my condors.
I have .25, .257, and .308. All use TJ barrel liners.
.25 has a 24" TJ .25 auto barrel with 1:14 twist. It is set up with a modified etac-reg with a large chamber on a 62 ci tank. Reg is set at 1800 psi and it gets 100+ shots starting in the 930's and ending in the 920's. I can change the TH setting with a shim and get anywhere from 890 to 960 fps.
Shroud is all aluminum and is 5 pieces that all screws together.
(http://i1192.photobucket.com/albums/aa340/dyotat100/20131225_124204_zpsirhak46r.jpg) (http://s1192.photobucket.com/user/dyotat100/media/20131225_124204_zpsirhak46r.jpg.html)
.257 has a 32" 1:14 TJ barrel. It runs one of my custom .257 valves in a tank adapter(etac but I make my own) in a 62 ci tank. .257 and .308 use a hammer cooking setup were the hammer clocks the gun instead of the breech. Hammer is barrel riding and 150 gram. Breech is aluminum and is just a open and shut to load. Aluminum doesn't work on the breech if you have to cook the gun with it but works great now that there is no load on it. Shroud is same as .25 but just longer for the longer barrel. Here is some numbers
3300 psi fill gets shots in the 1080's with 74 gr lyman. With 102 gr slugs it is in the 960's.
3950 psi fill gets shots in the 1140's with 74 gr lyman. I got 1060's with 93 gr. I didn't shoot the 102 gr on 3950 because all my tanks were low.
(http://i1192.photobucket.com/albums/aa340/dyotat100/20140131_204658_zps4hifzuze.jpg) (http://s1192.photobucket.com/user/dyotat100/media/20140131_204658_zps4hifzuze.jpg.html)
.308 has a custom 32" 4 groove 1:14 that I had made. It uses my custom .308 valve in a tank adapter in a 62 ci tank. Runs a barrel riding 150 gram hammer also. Right now I haven't made a shroud for it yet.
3300 psi gets 980's with 118 gr and 158 gr goes right around 900 fps. 171 gr are in the 880's.
4000 psi bumps things up a bit. 118 gr go in the 1040's
158 gr are in the up 950's.
171 gr is right around 930 fps.
(http://i1192.photobucket.com/albums/aa340/dyotat100/20131230_202208_zps1urw92ra.jpg) (http://s1192.photobucket.com/user/dyotat100/media/20131230_202208_zps1urw92ra.jpg.html)
(http://i1192.photobucket.com/albums/aa340/dyotat100/20131221_092317_zps6yfpwa1q.jpg) (http://s1192.photobucket.com/user/dyotat100/media/20131221_092317_zps6yfpwa1q.jpg.html)
I have to change my hammer springs to get back my bell curve on both guns. The .257 at one time would get 5 shots
1066 1070 1072 1065 1062 on 3300 psi. On the HPA tank I can get a curve and was surprised how it was shooting during the crony testing.
I took all 3 out today to do a little shooting. .25 was struggling in the wind but was still able to hit a couple golf balls at 110 yds.
.257 shined in the wind. I was drilling the golf balls at 110 yds. .308 needs a muzzle brake to calm the beast. It does great but it is a monster. I have a muzzle break that I will put on until l do a shroud.
Here is the one golf ball that I stuck in a fitting and couldn't go anywhere. This was shot standing shooting off a high table at 110 yds.
(http://i1192.photobucket.com/albums/aa340/dyotat100/20140314_142503_zpsnzvs8wrq.jpg) (http://s1192.photobucket.com/user/dyotat100/media/20140314_142503_zpsnzvs8wrq.jpg.html)
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Here is the .257 build link.
http://talonairgun.com/forum/viewtopic.php?f=11&t=24826 (http://talonairgun.com/forum/viewtopic.php?f=11&t=24826)
Here is the .308 build link.
http://talonairgun.com/forum/viewtopic.php?f=11&t=21357 (http://talonairgun.com/forum/viewtopic.php?f=11&t=21357)
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Is your # still the same as last year?
How about the same design setup as your .308 but with the .25 ACP barrel for shooting 52 grain slugs around 80-90 ft lbs?
I would need the last 4" of the muzzle turned to exactly .437" (unless you're aleady using that barrel diameter) - I have a 1.5" x 13" long Titanium Clague I could put on it........
Let me know....
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Yes same number. Why do you want it to shoot so slow? 900 fps is 93 fpe.
With my valve it could do 1050 fps at least.
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Very nice guns and impressive performance..... I'm still interested in the pressure range used to produce given shot strings so I can get an idea of the efficiency if you have that data....
Bob
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I like to stay in the 950'ish range so I don't cross into the transonic region. The ranges I shoot at even 900 is just fine.
I want a fairly high shot count at that power level.
Right now I get 10 shots within 2.5% @ 80 ft lbs. out of 290cc's.
62 ci ought to be an entire day of pesting with no need to top off or bring a pump!
I will text you tomorrow after work...
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Thanks
Here is all I have. .25 shooting 63 gr and .257 shooting 74 gr
(http://i1192.photobucket.com/albums/aa340/dyotat100/image-1_zpsqd7po01_edit_1394855604415_zps7zftzrm7.jpg) (http://s1192.photobucket.com/user/dyotat100/media/image-1_zpsqd7po01_edit_1394855604415_zps7zftzrm7.jpg.html)
Let me know what else you need or want.
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*Edit*
I didn't see the bullet weights on top.........Thanks!
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Thanks for that, I assume they both are running 62 CI tanks, so I'll run the numbers....
.25 cal, 6 shots, FPE = 142, 142, 139, 137, 134, 134, total is 728 FPE
Pressure drop is 3122 - 2809 = 313 psi which is 313 / 14.5 = 21.6 bar times 62 CI = 1338 CI of air total at 1 bar
Efficiency = 728 / 1338 = 0.54 FPE/CI
.257 cal, 6 shots, FPE = 191, 191, 187, 185, 184, 181, total is 952 FPE
Pressure drop is 3205 - 2860 = 345 psi which is 345 / 14.5 = 23.8 bar x 62 CI = 1475 CI total at 1 bar
Efficiency = 952 / 1475 = 0.65 FPE/CI
Appreciate the data....
Bob
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Bob, on the 25 I got the following: (I may have missed the 1 BAR addition for volume and just calculated space though)
1 ci = 16.387064 cc's - so 62 ci = 1016 cc's
Efficiency = .61
26.9 BAR/CC
135.8 ft lb Avg
52 psi/shot
I bet it would run closer to 1.0 in the 80-90 ft lb range. Just a TH adjustment could take care of that.
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So what is good and what is bad?
I can do the .308 if you want tomorrow.
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Bob is the Master on this subject, but basically you want an efficiency factor of 1.0 or higher.
Your numbers are typical for a high power big bore that isn't tuned for a good bell curve but is tuned for maximum output - unfortunately wasting a lot of air.
You could tune it down and only lose marginal power but gain a ton more shots.
I didn't understand any of that when I first strted following Bob's posts.
Now that I do, my guns are all tuned for the best compromise of power and shot count.
I'm sure he will explain finding the 'knee' of the bell curve and tuning to just below that.
You want the valve closed by the time the pellet hits the halfway mark down the barrel. Any longer of an opening duration and you're wasting air.
You would have to adjust your top hat down maybe .005" at a time and shoot a couple of shots over the chrony.
You will see where the velocity does not drop much at first then begins to drop suddenly - that is the 'knee'.
You want the gun tuned at or just below this point for maximum efficiency.
If your throughput in the top hat matches the bore diameter it will make it even easier.
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I can get a bell curve. I just haven't adjusted to the new hammers in .257 and .308. I will have to change out the hammer springs in both. The .257 use to get a good curve. If I go up to 3600 psi I can get a good curve right now.
.25 numbers are from my .25 when it had a 24" LW barrel in it with my one off valve. That valve at one time did over 1000 fps with 70.5 gr. Yes the stem bore is .250" also. .257 is .280"
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Upping the fill pressure to get a curve shows there is too much hammer spring (as you already stated).
I am using an 82 gram hammer I made in my 25 Challenger with a 10# hammer spring.
The only way I can tune my gun is by adjusting the hammer spring preload using my rear velocity adjuster.
The heavy hammer gives me a longer dwell = longer valve opening duration.
That is all I can readily control.
You on the other hand can control hammer spring preload just like me BUT you can also adjust how far the valve actually opens. That is something I really like about the Condors.
Hammer weight/spring preload can control duration (time on target). The heavier the hammer the longer (in milliseconds) it takes to reverse direction.
Top hat controls how far the valve opens - either adjust the top hat itself or add shims in the form of o rings or teflon washers behind it.
Because you can adjust those components you have way more control over tuning your rifles than I do.
I would love to have one of those to tinker with! ;D
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If you have the ability to raise your fill pressure safely, then that is the easiest way to get a good bell-curve.... HOWEVER, 62 CI tanks are usually rated at 3000 psi.... If that is the case WHAT are you doing filling them to 3600.... or as in your original post, 4000 psi ???.... Enlarged from your posted photo....
(http://i378.photobucket.com/albums/oo221/rsterne/Important/20131225_124204_zps90f2b056.jpg) (http://s378.photobucket.com/user/rsterne/media/Important/20131225_124204_zps90f2b056.jpg.html)
The GTA cannot condone these sort of practices, it is only a matter of time before somebody reading a thread that suggests it gets maimed or killed.... BTW, I noticed that in your build threads you talk about using Helium.... I assume the numbers you gave above were on air?....
Bob
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That is my regulated .25 setup.
I haven't shot the .257 on helium yet. .308 did over 400 fpe on 3000 psi of helium in the very early stages of my valve. It should do over 500 fpe now.
(http://i1192.photobucket.com/albums/aa340/dyotat100/20140315_131232_zpstzco7vwf.jpg) (http://s1192.photobucket.com/user/dyotat100/media/20140315_131232_zpstzco7vwf.jpg.html)
I have a 70 ci 4500 psi bottle I use. The highest I fill is 3300 on the 3000 psi bottles.
I'm in the process of figuring out a 45 ci 4500 psi bottle setup with a small chamber. They are to short so I'm going to build a 2" OD × 3" long chamber to add more volume and length. Bottle will be offset on the chamber to drop the bottle down.
I'm going to build a 1:10 7 mm and it will be a 4000 psi gun.
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All the photos you have above show the same tanks, a 62 CI, which is 3000 psi.... A 10% overfill is not recommended, the 3000 psi stamped on the tank is there for a reason.... it is the Maximum Safe Working Pressure (MSWP).... I assume the strings you posted were with those tanks, if you were using a 70 CI tank, then the efficiency calculations I did were 13% better than you actually got if you used the larger tank.... CarsonRatSniper's comment about 1.0 FPE/CI being "OK" is about right for a .25 to .30 cal that is shooting a proper bell-curve with a 4% ES (ie starting about 4% below peak and ending there), but not stellar performance by any means.... The kind of numbers you have (~0.6 FPE/CI) are about what I would expect for a gun tuned as per your strings, where you are basically getting a few shots right at the top of the curve, the first two being equal in velocity.... I've certainly seen Big Bores with a lot worse efficiency, my DAQ .308 Exile only got 3 shots as delivered, 186 FPE (118 gr.) at 0.38 FPE/CI.... With just a simple reduction in hammer spring it now gets twice the shots at a higher average velocity at 0.88 FPE/CI from a 3200 psi fill....
I've never used Helium, always been curious about it, and realize it's in a class of it's own FPE-wise.... What wall thickness and material are you building your pre-chamber from?....
Bob
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I never leave a tank with more than 3000 psi in it.
Shot strings were done with 62 ci.
Chamber will probably be out of 1144 shock proof. Has a strength of 125,000 psi. Comes in bar and I will bore it. Would have .120" thick walls and OF would be 2"
I also have 7075 aluminum bar but I have to look up the strength. What material would you use for a chamber good for 4500 psi?
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My info on 1144 is 108K yield and 125K tensile, but even at the lower figure, at 4500 psi the safety margin is ample at 3.3:1 for a 2" OD with a 0.120" wall.... My usual choice is normallized CrMoly, but at 63K yield and 97K burst it would require a thicker wall to have sufficient safety margin at yield, although at burst it would be nearly 3:1.... You can use 7075 with sufficient wall thickness, but I don't have the data for that.... Lloyd Sikes would be the guy to ask, you can pm him at lloyd-ss here on the GTA.... I guess the nice thing about boring a piece of bar stock is that you can machine in one end and not have to install a plug with fittings, O-rings, etc....
You might want to check out the "Geek Gate" as we call it here on the GTA.... http://www.gatewaytoairguns.org/GTA/index.php?board=164.0 (http://www.gatewaytoairguns.org/GTA/index.php?board=164.0)
Bob
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is there a smith that will build that .257 .
those numbers are amazing, think id buy one if they came stock like that....would make an amazing coyote rifle round here
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Thanks
There are 2 1144 materials. One is stress proof and says 100,000 and there is shock proof that says 125,000.
I will use the shock proof.
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Is that tensile strength, or yield strength?....
Bob
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Says yield strength.
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Did a little casting today.
(http://i1192.photobucket.com/albums/aa340/dyotat100/20140315_193225_zpsneva1jt0.jpg) (http://s1192.photobucket.com/user/dyotat100/media/20140315_193225_zpsneva1jt0.jpg.html)
(http://i1192.photobucket.com/albums/aa340/dyotat100/20140315_193847_zpsuvrxyo9g.jpg) (http://s1192.photobucket.com/user/dyotat100/media/20140315_193847_zpsuvrxyo9g.jpg.html)
Cast 600 257-420 and then made a new sprue plate with smaller holes and cast 650 with it. New plate has .108" compared to .150" that it came with.
(http://i1192.photobucket.com/albums/aa340/dyotat100/20140315_194721_zpsu3oaouvi.jpg) (http://s1192.photobucket.com/user/dyotat100/media/20140315_194721_zpsu3oaouvi.jpg.html)
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Nice looking boolits.... I've found that the sprue hole shouldn't be larger than 50% of the diameter of the base or you can get a distorted/squashed corner....
Bob
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Another interesting material is 7068 aluminum, it has a yield of 95,000 psi and is available in round bar. It's generally referred to as ordinance grade; maybe not the best moniker for a pressure vessel.
https://online.kaiseraluminum.com/depot/PublicProductInformation/Document/1033/Kaiser_Aluminum_Alloy_7068_Brochure.pdf
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The small sprue plate hole is catching on...:) be nice to see Lyman and RCBS split it up that way...25 and below get .1" plates and the rest can get bigger. It sure makes a diff for the .224 stuff, but it was the 25 auto stuff that got my notice...the size witness would be missing a crescent of area upstream of the sprue cutter where it had effectively bent the boolit on the cut off.
cheers,
Douglas
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Yeah I have been doing it for awhile. Ever since I bought a mold from Veral and saw how small his holes were.
I have a Lyman 4 hole .308 mold that I have .104" holes on and it makes perfect bullets also. I also have a 4 holes Ideal 257420 mold that has .175" holes. Uses the same plate as the .308 does. I used the plate from the .308 but still had issues with bullets not coming out perfect so I'm still using my Lyman 2 hole mold. Was hoping I could use a 4 hole mold on that bullet because it is what i shoot the most.
The 4 hole 118 gr .308 is my best bullet so it worked out there though.
I have also done it for a 4 hole NOE 257 mold for someone else and it made it work great. Opens with your hand instead of a hammer.
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Here you go Bob.
70 ci tank
83.3 gr
3490-1020 fps
3448-1028 fps
3404-1031 fps
3361-1038 fps
3318-1031 fps
3274-1027 fps
3228-1028 fps
3172-1028 fps
3120-1019 fps
3070-1020 fps
3022 ending pressure
10 shots 468 psi
Here is my setup. Gauge is +- .025%
(http://i1192.photobucket.com/albums/aa340/dyotat100/20140318_123501_zps0vvcdplk.jpg) (http://s1192.photobucket.com/user/dyotat100/media/20140318_123501_zps0vvcdplk.jpg.html)
Also got 1083 fps with 94 gr 4000 psi for 244 fpe
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I didn't calculate the average, just guessed that it was ~1025 fps (194 FPE) so a total of 1940 FPE.... 468 psi / 14.5 = 32.3 bar x 70 CI = 2259 CI.... Efficiency = 1940 / 2259 = 0.86 FPE/CI.... pretty decent, but I've never run a gun at those pressures to compare....
Bob
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Thanks
I threw out 1,9, and 10 and I came up with 97.
That was my first attempt at a curve. If I spent some time I could get a better curve.
Once I get a 4500 psi setup I will play with it some more. If I have time I will change out the hammer spring and do a curve with my 3000 psi tank. I will do 5 shoot string from now on.
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I threw out 1,9, and 10 and I came up with 97.
No idea what that means (the "97").... I don't see anything wrong with a 2% ES (2% of 1038 = 21 fps, so a low of 1017) for shooting at about 100 yards, the vertical stringing should be minimal.... and you're within that with the string you posted.... It would be interesting to tether the gun to a 3000 psi regulator and see what the ES is that way....
What weight did your 257-420s cast at?.... The ones I did using 1% tin were 73.5 gr.... I have one cavity converted to a Hollowpoint and it drops at 66.0 gr....
Bob
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97 fpe/ci is what I got dropping 1st, 9th, and 10th shot. I will be making a reg setup also and set the reg around 3000-3200 psi.
Should be able to get 25 shots on 4500 psi tank.
I have HP 420 mold also. It drops 69.4-69.5 real consistent.
Regular 420 mold drops and 73.9-74.3. Most right around 74.
This is with pure lead.
Here is a NOE mold that has been shaved down and now produces 67 gr HP and 71 gr regular.
I poured these last night.
(http://i1192.photobucket.com/albums/aa340/dyotat100/20140319_115455_zps3xcp0ubq.jpg) (http://s1192.photobucket.com/user/dyotat100/media/20140319_115455_zps3xcp0ubq.jpg.html)
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I just noticed a problem with your pressure data, which would cause you to get different results.... You missed reading the pressure after shot 8, the pressure dropped 102 psi instead of 50ish.... for 10 shots you should have 11 pressure readings.... 3490 - 3022 = 468 (about 47 psi per shot).... If you drop out the 1st, 9th, and 10th shots, the starting pressure is 3448 but after the 8th shot the pressure should be about 3121 psi, not 3070, that would be after the 9th shot, and 3022 after the 10th....
So for 7 shots @ 1030 fps (196 FPE) = 1372 FPE.... pressure drop 3448 - 3121 = 327 / 14.5 = 22.6 bar x 70 CI = 1579 CI.... 1372 / 1579 = 0.87 FPE/CI....
Bob
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Yep no pressure after last shot.
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EDITED above - I found the problem....
Bob
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Thanks. I fixed it on original post.
You were close. I went out and dug the paper out of the trash. It is 3120 psi.
I'm liking all the technical info and support here. Anybody good with how to build a good trigger setup?
I'm going to build a complete condor frame setup for .457. The trigger is my only issue and would like to do something better.
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I believe RL airgun supply offers a read to shoot .257 Condor.
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http://www.rlairgunsupply.com/custom-shop-page-2/ (http://www.rlairgunsupply.com/custom-shop-page-2/)
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My post says .457. I'm building a COMPLETE gun, frame and all.
What R&L offers is not a real .257. It is still powered by a .25 condor valve.
My .257 barrel has a .375" breech and the valve has a .280" ID. Condor valve is .247" OD .217" ID.
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hit a couple golf balls at 110 yds.
Maybe next time out you can shoot some paper so we can tell something about the accuracy.
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Did you find any advantage going over the boresize on the valve, ie .280 on a .257".... I know nothing about Condors, is there a stem in the way of the flow?.... If so, what is the diameter, and hence what is the remaining area at the smallest restriction?....
My .257 Hayabusa is running boresize porting right through.... The barrel port is 0.188 x 0.312", the transfer port is 1/4", the valve exhaust port is 1/4", and the valve throat is 0.281" with a 0.115" stem (0.256" equivalent)....
Bob
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I don't have a good place to shoot paper or the time.
I just let Tofazfou, knife maker, and 80 grit over on TAG do all the paper punching. Those are all my builds also.
I will contact the guy in Greece I built a 1:10 30" setup for and ask for some pics. He is shooting out to 400 yds.
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The valves I sell are .260" bore.
My .257 setup has a .280". At the time I was building it I was opening it up .010" at a time. I can't remember if it changed from .270" to .280". I just left it the way it is today. I need to put one of the new valves in my gun and see what it shoots.
I might be surprised and gain even more fps ;)
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Is there a stem in the Condor valve?
Bob
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is there a stem in the way of the flow
the "top hat" is essentially a cross drilled thin walled tube once the poppet is opened. Also the whole tank is a huge, straight shot plenum with a funnel shape focusing the air flow right to to the poppet at the end of the tank. The smallest restriction could end up being the straight open end of the barrel.
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http://talontunes.com/shop/quick-change-top-hat/ (http://talontunes.com/shop/quick-change-top-hat/)
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Here is a drawing showing the basic hammer/ breech slide/ top hat design of the AirForce.
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http://www.stealthresource.org/introduction.htm (http://www.stealthresource.org/introduction.htm)
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The only limit to the size of the poppet and top hat would be leaving enough material in the valve body to thread into the bottle. The id of the frame tube is 1.000 inches so this is the limit for the od of the hammer. There was a group buy for custom medium diameter 4,500 psi carbon bottles but I don't know how they intend to conveniently fill them to shoot that high.
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The valves I sell are .260" bore.
Is there an after market hpa bottle version of your valve that you sell. The Airforce bottle/ valve are over priced at $200.
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Thanks, I think I understand the airflow path now....
Bob
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That drawing makes it look like there is a spring inside the bore of the top hat but what he is really trying to show is that the tube is threaded on the end so the collar can screw up and down to set the max valve lift.
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Here are the differences between the stems. Stock condor on the left, my .25, .257, and .308.
(http://i1192.photobucket.com/albums/aa340/dyotat100/20140320_185303_zpscju3j9xl.jpg) (http://s1192.photobucket.com/user/dyotat100/media/20140320_185303_zpscju3j9xl.jpg.html)
Here is a stock condor stem inside my .257 valve and my .25 inside my .308 for a size comparison. A stock stem will fit inside my one off .25 valve that made 170 fpe with 89.5 gr in 24" barrel.
(http://i1192.photobucket.com/albums/aa340/dyotat100/20140320_185354_zpsbokji54c.jpg) (http://s1192.photobucket.com/user/dyotat100/media/20140320_185354_zpsbokji54c.jpg.html)
A stock condor valve is more than enough to shoot pellets but not enough for 70 gr slugs.
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What actually controls the airflow.... ie where is the seat that seals?.... I'm still having difficulty understanding that....
Bob
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Here is a old pick of my first .308 valve.
(http://i1192.photobucket.com/albums/aa340/dyotat100/NewCondorValve051_zpsrzxgrn3d.jpg) (http://s1192.photobucket.com/user/dyotat100/media/NewCondorValve051_zpsrzxgrn3d.jpg.html)
I'm out of town working and will be home Saturday and can get pic's of what ever you want then.
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OK, that changes things considerably.... What is the diameter of the hole in the valve body that contains the moving "top hat / valve stem".... and what is the diameter of the stem itself.... It looks like the hole in the valve body is the same size as the OD of the rear portion of the top hat.... That would mean that the throat is the same diameter as the OD of the smaller (rear) portion of the top hat and then you subtract the area of the stem, correct?.... I assume that area works out to larger than the ID of the top hat, but I'd like to see the numbers.... Once the top hat is inside the valve body, the area for flow is the ID of the valve body MINUS the stem and/or the web between the angled cross-holes, whichever is the largest at any given point....
In terms of lift, what are you allowing, at least 25% of the throat (seal) diameter?.... Less lift than that restricts the flow because of the "curtain height" effect.... Once poppet valves have a lift greater than 1/4 of the throat diameter, their flow rate can't increase because the limiting factor is the throat area instead of the curtain area....
Bob
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The stem that you see at the end of the top hat is buried in the poppet. The next thing the air sees when the valve opens are the two holes. Which, since his are on an angled surface, could have a combined area greater than the id of the top hat bore. The spring perch is trick also. This is beautiful work. The original factory valve is simply cross drilled. Though that looks like an old version factory valve. There is a new, high flow valve which has a different poppet and top hat. The other possible tight spot in the design could be the space between the inlet bore that the poppet moves back into, and the poppet od. But this looks to be more than generous also.
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The stem that you see at the end of the top hat is buried in the poppet. The next thing the air sees when the valve opens are the two holes. Which, since his are on an angled surface, could have a combined area greater than the id of the top hat bore. The spring perch is trick also. This is beautiful work. The original factory valve is simply cross drilled. Though that looks like an old version factory valve. There is a new, high flow valve which has a different poppet and top hat. The other possible tight spot in the design could be the space between the inlet bore that the poppet moves back into, and the poppet od. But this looks to be more than generous also.
You obviously don't know much about AF valves. All my valves are custom made. Not a modified valve. The valve in the picture is a .308 valve. It is a lot different from a AF valve.
Ok Bob here are some numbers for you
.25 valve
.310" opening
.100" stem
.375 seal
Stroke .115" (.135 on my one off valve)
.257/.308
.320" opening
.100" stem
.375" seal
Stroke .257 .115"
Stroke .308 .085"
I did a little porting on my .308 and it caused tank dump after 5 shots with 158 gr. It is now at .070" and still makes the same power and no more tank dump.
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All my valves are custom made. Not a modified valve. The valve in the picture is a .308 valve. It is a lot different from a AF valve.
Not sure where that came from...
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You are doing beautiful work. Want to sell me one?
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By "opening" do you mean the ID of the throat, downstream (forward) of the seat?.... or do you mean the ID of the hole through the top hat?.... Is the 0.375" "seal" the OD of the plastic poppet, or the ID of the throat where the seal occurs?.... Sorry for all the questions, but I've never been inside a Condor and want to understand them.... I would agree that the area of the angled ports are greater than the ID of the top hat.... Looking through the top hat you would "see" a restriction from the web between the holes, but by the flow "bending" a bit it wouldn't notice it.... The (thin part of the) stem still subtracts some area from the throat, however....
You certainly have plenty of lift on the .257 valve.... If the seat is 0.375" then you will continue to get increased flow up to a lift (stroke) of 0.094", although that may be a moot point as the ID of the air path is quite a bit less than that anyway.... so that 0.094" would be a maximum that would benefit you from a lift point of view.... However, increasing the lift further also increases the dwell of the valve, enabling more air to flow through it during the shot cycle....
I'm curious about your "tank dump" problem on the .308.... It sounds like a hammer bounce situation, re-opening the valve and causing the tank to drain once the pressure drops to a given level.... I had a similar situation on my first 9mm Disco Carbine when I tried a very light valve spring.... The shots went.... POP.... BANG.... B-BANG.... B-B-B-BURP.... BBRRAAAPPPPPPPPPPPPPPPPPP.... *LOL*.....
Bob
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Yes the opening is where the air comes in the valve then goes to the ports in the stem. I use 3 ports instead of the 2 AF uses for ease of manufacturing.
One of the main contributing factors to tank dump is the step in the barrel to bore size. With .25 you have a .250 bore and the barrel is .308".
so barrel is real thin and there is no step.
With .257 I machine the barrel to .374". I tried when I first built the .257 to use a .25 valve and I never got it to work. Even with 60 lb return spring the best I got was 1000 psi for the first shot(partial tank dump).
I then down sized the .308 valve a little and have never had a problem.
.308 barrel is .428" with .308 bore so the step is big also. But throw in heavy bullets and the tank dump gremlin is there. It took me some time and a lot of making parts and pieces to get where I an now.
There is some weird things that happened with these valves. If I take a .308 stem and open up the ports it will tank dump. On a .257 or .25 you can port all you want. .257/.308 valve has a 49 lb return spring. I'm sure I could use a smaller one on .257 but I got to a point where I was tired of experimenting. .25 valve will work with almost no spring.
I'm going to build a .308 with a .374" breech so there will be only .033" instead of .060". Should make it so I can shoot 200 gr bullets.
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You have a very different set of closing forces to work with than in a "conventional" valve where the end of the stem is exposed to atmospheric pressure and the area of the stem times the reservoir pressure provides the closing force.... In a gun with a 5/32" stem at 3000 psi, that works out to 57 lbs., plus another 7-10 lbs. for the spring.... In your case, if I understand it correctly, there is an O-ring sealing around the front of the top hat, so if that diameter is larger than the rear portion, then you have a net OPENING force.... Once the valve is open, the pressure on both ends of the top hat is essentially the same, so the opening force is that pressure times the area of the front stem of the top hat, while the closing force is that pressure times the area of the rear stem.... unless I'm not understanding it correctly.... That would sure explain the tendency to dump the tank....
Bob
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NT
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then you have a net OPENING force.... That would sure explain the tendency to dump the tank....
Until the pellet leaves the barrel. The AirForce airguns are not noted for their efficiency. But they do have a big tank. And there aren't too many off the shelf .25 cals that you have to reduce the fill and turn down the tune to keep them under 70 fpe with pellets as you do with a new high flow Condor.
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I still don't think you would have much of a pressure difference across the top hat.... Maybe my suggestion is wrong, but I still think it is possible.... I notice that one of the top hats linked to has the sides milled away, and possibly a flat as well.... maybe to avoid this?....
Bob
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Even the stock high flow valves will apparently dump the tank if the stroke stop is set too high. This is from a review on Pyramyd.
" The tophat is held in place by 2 small screws. If it is too far forward when you engage the cocking lever the whole tank can discharge. Just loosen the screws and screw the top hat in the direction that moves it closer to the tank. Solved the problem."
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I notice that one of the top hats linked to has the sides milled away, and possibly a flat as well.... maybe to avoid this?....
I don't think the large diameter flat of the top hat is under barrel pressure. It is at atmospheric, sealed off by the oring of the breech closing slide. Which is actually a giant, sliding, transfer port. Transferring the strike of the hammer to the valve. And transferring the air to the barrel. But there is some area and volume of material at the smaller diameter of the tophat inside the slide for the barrel pressure to turn and build at the base of the barrel and pellet and work against. And some further opening force could develop from the volume of material of the barrel which is sealed inside the slide at the other end which would want to continue to force the slide back toward the valve. Now that I think of it, this would be a much greater volume than end of the tophat. To increase efficiency you might want to cut the oring onto the barrel as far back as possible instead of into the id of the slide. Or make sure the tolerances are set so the oring in the slide is very near to falling off the end of the barrel when the valve is fully opened.
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Volume doesn't matter for force, only the area exposed to the pressure ( ID of the O-ring) at both ends.... If the front of the top hat is bigger than the back, you have a net opening force, IMO....
Bob
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I can see what Bob is getting at, and I can see a possible solution. Make the "brim"of the top hat longer, recess the valve body for it and put the O-ring in the recess. That would expose the back of the "brim" to tank pressure while the valve is open. Causing a net closing force to the valve.
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Volume is just area in 3D. Same thing. When the air pressure that is past the poppet in a common airgun valve is trying to spit the stem back out to the atmospheric side of the valve body toward the striker, it is trying to reduce the matter that is inside. The pressure pushes on the surface area but it is trying to get rid of the additional volume.
Edit:
I guess the simpler way to look at it is that there is a cross section of piston in a bore that can move, so when something pushes on it, it moves. And the volume aspect of the piston would only make the force progressive if it were a significant fraction of the air space volume.
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expose the back of the "brim" to tank pressure while the valve is open. Causing a net closing force to the valve.
I think this would be the same as increasing the stiffness of the steel spring.
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You could actually reduce the springs stiffness. This added area would only be active for the time the valve is open and would make the valve close sooner, increasing efficiency.
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Make the "brim"of the top hat longer, recess the valve body for it and put the O-ring in the recess. That would expose the back of the "brim" to tank pressure while the valve is open. Causing a net closing force to the valve.
The air that is past the poppet is flowing inside the tube of the top hat. You would have to cross drill the tube again just under the top hat to fill a new chamber in the valve body. Or slot some channels in the bore of the valve down into the seat. This would create a barrel pressure dependent closing force to balance the opening forces in the slide but is getting to be some fancy footwork.
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Make the "brim"of the top hat longer, recess the valve body for it and put the O-ring in the recess. That would expose the back of the "brim" to tank pressure while the valve is open. Causing a net closing force to the valve.
The air that is past the poppet is flowing inside the tube of the top hat. You would have to cross drill the tube again just under the top hat to fill a new chamber in the valve body. Or slot some channels in the bore of the valve down into the seat. This would create a barrel pressure dependent closing force to balance the opening forces in the slide but is getting to be some fancy footwork.
And the air is deadheaded against the O-ring that seals the OD of the top hat in the valve body. It is this O-ring I'm suggesting relocating.
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Good concept.
This is the more in line with the discussion Bob was trying to get started over here:
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http://www.gatewaytoairguns.org/GTA/index.php?topic=62679.msg600686#msg600686 (http://www.gatewaytoairguns.org/GTA/index.php?topic=62679.msg600686#msg600686)
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Maybe the moderators could move some of this valve theory over there so the OP could have his thread back.
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OK, after watching the video showing the quick-change top hat being installed I realize that the flats on the quick change top hat are only there to accept a 3/8" wrench.... It appears to me that the top hat must be sealed at both ends with an O-ring, correct?.... one in the valve body, and one in the sliding breech?.... There is a hole drilled through the top hat, so once the poppet is open, there is very little, if any, pressure difference between the ends of the top hat.... even if the pellet has left the barrel.... and the larger the hole through it, the less the pressure drop across it....
Therefore, as I see it, there are two opposing forces on the top hat.... From the front, the air pressure is pushing against the top hat at the ID of the O-ring inside the sliding breech, and therefore at the OD of the front portion of the top hat.... From the rear, the air pressure is pushing against the top hat at the ID of the O-ring inside the valve body, and therefore at the OD of the rear portion of the top hat.... then you subtract from that area the (smallest) diameter of the hole through the top hat (from both ends).... Here is an example:
Bore of top hat 0.250" ID: area is 0.0491 sq.in.
Front stem of top hat 0.350" OD: area is 0.0962 sq.in.
Back stem of top hat 0.300" OD: area is 0.0707 sq.in.
Effective area of front = 0.0962 - 0.0491 = 0.0471 sq.in.... at 3000 psi that is a force of 141.3 lbs.
Effective area of rear = 0.0707 - 0.0491 = 0.0216 sq.in.... at 3000 psi that is a force of 64.8 lbs.
This becomes an net force pushing the top hat back into the valve body of 141.3 - 64.8 = 76.5 lbs.
If the rear stem was 0.350" and the front stem was 0.300", then that force would be forwards towards the breech.... If the stems were equal in size, there would be no net force.... If the rear O-ring was on the OD of the top hat, which let's say was 0.500" in diameter, the force towards the front (breech) would be much greater, in fact so great that the valve would tend to slam shut immediately.... It might even blow the top hat out of the valve body.... To me it seems clear that the relationship between the front and rear diameters of the top hat have a huge effect on the opening or closing forces on the valve.... If I am not understanding something, somebody please give me a smack....
Bob
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No smacks from me. ;D ;D ;D You saw what I saw. You just put the numbers to it. ;D ;D A stepped top hat may be the right answer.
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or simply increase the diameter of the back stem or decrease that of the front stem until you get the forces you need.... If you don't want ANY net force, so that the spring does all the work, then just make them the same size....
Bob
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Is there also some force generated from the pressure working against the cross section area of the base of the barrel?. The barrel is the piston and the sleeve is it's cylinder. If there is force across the area of the piston (barrel and pellet), but the piston is held fixed (the pellet can start to move but not the barrel) and the cylinder is free to move, won't the cylinder (sleeve) try to move back against the top hat adding to the opening force?
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Only if the O-ring ID at the back of the sleeve is larger than the O-ring ID at the front.... If they are the same size, it works just like a fill probe, there is no net force trying to push it out of the gun....
Bob
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I see. The area of the slide that the barrel pressure could act on to move it is occupied by the top hat which is getting the force instead.
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I see. The area of the slide that the barrel pressure could act on to move it is occupied by the top hat which is getting the force instead.
I see your misconception. ;) Pressure acts in all directions. Force can be seen as "pressure given a specific direction". The forces on a valve system act only in a linear direction. Therefore only the ends of the top hat will "see" the pressure as a force. Whichever end has the larger area will generate the larger force.