GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: lloyd-ss on March 22, 2016, 01:45:57 AM
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++++++++ EDITED by Lloyd-ss on 31 March 2016 with new post of 2162 FPS shot. See Reply # 33 for info.+++++++++
We've had a thread going in the R&D gate about what the maximum possible velocity of a PCP on air might be.
http://www.gatewaytoairguns.org/GTA/index.php?topic=102604.240 (http://www.gatewaytoairguns.org/GTA/index.php?topic=102604.240)
There is a lot of mumbo jumbo and theories floating around on mainly other airgun forums about "things" that limit the velocity of a PCP. Some had the theoretical limits as low as 1600fps. I don't think any of the guys on this forum were too keen on believing there were such artificial limits. Me personally, I always thought the limits were junk theories.
Anyway, don't tell me it can't be done. ;D
The video shows, and explains the shot.
http://www.youtube.com/watch?feature=player_embedded&v=JWt5DnfYH3I # (http://www.youtube.com/watch?feature=player_embedded&v=JWt5DnfYH3I#)
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(http://upsidedownmoon.tripod.com/sitebuildercontent/sitebuilderpictures/icon_nworthy.gif)
That is the highest fps I read anywhere on air. Well done.........wow.
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Thanks Mike.
I've heard a lot about what CAN'T be done, but I haven't heard much about what HAS been done.
And the 2031 fps shot was with a 9.1 gn pellet. Light for a .278, but it is still 83 fpe.
Lloyd
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Holy Smokes !!!
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WELL DONE LLOYD !!!
Bob
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O' yea .... records standing or hear-say to limits are No More !!
Well done lloyd
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thats COOKING!!!!! wow ya know it wasn't as loud as I thought it would be!! efficient use of the plenum size and barrel length??
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JEEZ!!!! Lloyd give Lloyd some air and a barrel. Just Wow!! David
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Lloyd,
Impressive. It is all I can say.
Daniel
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Very cool 8)
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Cool!
I bet diablos wouldn't like that speed at all.
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thats serious. wow good job sir.....
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Thanks guys, for the words of encouragement. This has been a fun project and I think it shows that there is still a lot of un-tapped potential in PCPs. The pellet release mechanism is key to the high vel in this set-up. Letting the pellet get 100% of the air pressure behind it before it starts to move.
Lloyd
P.S. Michael M and David, I plan on bringing this contraption to the Funshoot in Kentucky in May. With that 47-1/2" long barrel we might have to call it the Kentucky long rifle while its there. I have no idea if it will hit the broad side of a barn, though. ;)
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Cool!
I bet diablos wouldn't like that speed at all.
Hard to say. They've never been shot that fast before, LOL. ;)
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Very nicely done Lloyd. Congrats, & thanks for pushing the limits of whats possible. Without guys like you I think the world might be pretty mundane.
And you are quite correct in your thinking, if the pellet can be held in place in the barrel & form a good seal until the maximum pressure & volume is behind it, then that would be the best way to make use of the fullest potential of the KE in the air behind it.
Also I feel the smooth bore barrel helped a little, & I am getting the feeling that friction from the oring may have robbed you a little velocity, but nothing much to worry about/cry foul over.
I can't wait to see what's next
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Am I the only one who thinks our airgun community should proceed with caution before implementing This further?
Otherwise the government will restrict air rifles even more.
But congrats and thanks for pushing the envelope!
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Am I the only one who thinks our airgun community should proceed with caution before implementing This further?
Otherwise the government will restrict air rifles even more.
But congrats and thanks for pushing the envelope!
Thank you for the congrats, but Please, in the interest of not hijacking the thread, if you want to have such a discussion about government regulation, start another thread. This thread is about the challenge and the fun of getting high velocities out of airguns. 'Nuff said! ;)
Thank you,
Lloyd
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I don't think you need to worry too much about "implementing" supersonic airguns.... The combination of the lightweight pellet required, and the corresponding low BC, will insure that the pellet is subsonic again before travelling more than a few yards.... You would get to alarm everyone with the report / shockwave, only to get none of the benefits.... *LOL*.... My guess as to downrange velocity would be about 1100 fps at 15 yards and 650 fps at 50 yards....
This experiment is basically for two reasons.... to put to rest the idea that the limits previously proposed for PCPs (sonic choking, molecular velocity) simply do not apply.... and to further our understanding of the Internal Ballistics of PCPs to improve our mathematical models of the same.... Interestingly, the Spreadsheet Lloyd has been using for several years is, so far, right on the money in predicting the performance we are seeing.... within less than a 1% error....
Bob
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.............. *LOL*.... My guess as to downrange velocity would be about 1100 fps at 15 yards and 650 fps at 50 yards....
................................
Bob
Dang it BOB! ;) Are you putting up a challenge! ;D
A redesign of the projectile, while keeping the release technique the same, just might do it. Of course shooting such a thing at 50 yards and not hitting the chrony might be more of a challenge. Hey, can I borrow your chrony, or maybe two of them?
Lloyd
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That is awesome. Nice work.
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Snortin right along Lloyd...well done.
Did notice you filled rather quick and fired right away...curious if you have means to measure the air temp within the reservoir....
Al
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I would love to see you Guys in chat on this just for a few hours if not less.
The instant interaction is fantastic.
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Snortin right along Lloyd...well done.
Did notice you filled rather quick and fired right away...curious if you have means to measure the air temp within the reservoir....
Al
Al, no, I did not check the block for any heat when I filled it. The block is 1 lb 10oz of aluminum so it will absorb and disperse the heat pretty quickly. Next time I take a shot I will monitor a few of the technical details better. I filled the gun quickly and took the shot quickly for 2 reasons: (1). I was videoing it and didn't want to waste too much time and then have to edit the video which always raises questions about the validity of the video, and 2., This is a bare-bones prototype and I didn't want to take too much time and give the projectile o-ring a chance to extrude and leak.
More careful shots are planned and ideas on what seriously "needs" to be monitored are welcome.
Lloyd
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Gotta love the "can do" spirit on this forum. :) Congratulations, Lloyd! Now, what'll it do with a lead projectile? ;D
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Cool!
I bet diablos wouldn't like that speed at all.
Hard to say. They've never been shot that fast before, LOL. ;)
Very impressive! Well done! I recall a Lyman black powder manual that showed round balls made from soft lead start to flatten out due to air pressure alone after they get above 1800 or 1900 FPS. For pure lead, 1750 is about as fast as you want to push it and by then leading has already become a problem. A well patched ball doesn't lead a barrel. I should add, I've heard that a round ball is the lightest projectile you can fit in a bore and a patch really is just a sabot. James Fenimore Cooper makes reference to using leather as a patching material.
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If there was a way to allow the pressure to come up before the round ball moved, a patched aluminum ball might be as light as you could go with sufficient strength.... but that would need the complication of a burst disc, and the uncertainty of how much energy it would eat up....
Bob
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Another idea for a projectile would be a sabot propelled airgun dart.
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Holding the sabot against the full pressure before firing is the problem I see.... Perhaps with such a long barrel this is less important, I don't know.... We are working with a total projectile weight (.278 cal) of just 9 grains, so achieving higher velocity would require less weight than that....
Bob
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Great job Lloyd ! This is where advances are made in this sport , with people willing to do the work to test the limits of what can de done!
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Yeah lets just call this a science project ;)
Very very interesting one though !
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very impressive Lloyd
job well done
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very impressive Lloyd
job well done
Dick,
Thank you. Still more to be done. Will be reporting in the coming weeks.
Lloyd
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Lloyd you, Rstern and couple of the other Brainiac's(hope I spelled it right) amaze me. You guy's come up with some of the best idea's and freely share them with the community. Well done and well played. I really wish I'd paid more attention in school now, but those pretty girls had my attention.............
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I've been working on this more (obsessed ?? :( ) and the progress has been a struggle. There might not be a lot of practical application to what I am doing but it shows what might become commonplace in the future. Years ago, airguns only shot 500fps, and that is ancient history now.
This is a special 46" long smooth bore .278 barrel and special breechblock that holds the projectile until full pressure builds up and then instantaneously releases the projectile. 2162 fps this time ;D . Yes, I realize that pellets don't fly well at high velocity, but this would be for lead bullets. And I realize that 2162 is too high of a velocity for lead bullets (supposedly) because the rifling will strip off the bullet, but this is not a powder burner with hot gas working at 30,000 psi. The acceleration is much slower and who knows, the rifling in the lead just might hold up.
I didn't make a video of this shot. For anyone interested in the boring details :P , there is a long thread going in the R&D Gate inside the Machine Shop Gate.
Here are a few pics I took of the 7075 aluminum alloy "pellet" that it is shooting, and a pic of the chrony after the shot. I recovered the pellet by shooting it into a tube about 18" long, stuffed full with plastic grocery bags, and positioned behind the chrony. You can see some of the plastic bags hanging out of the tube in the pic of the chrony. Good, clean, fun. Definitely keeping me off the streets.
Lloyd
(http://i226.photobucket.com/albums/dd79/loyd500/MaxVel%20Test%20Gun/3-26-16-1688/2162FPS-shot%20photo_zpsxcv4joto.jpg) (http://s226.photobucket.com/user/loyd500/media/MaxVel%20Test%20Gun/3-26-16-1688/2162FPS-shot%20photo_zpsxcv4joto.jpg.html)
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WOW!!!!!!!!!!
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WOW!!!!!!!!!!
Michael, I plan on bringing this to the FunShoot in May. I am looking for someone to catch the bullets, kind of along the lines of the guy in this video :o
https://www.youtube.com/watch?v=PASeTVPod5U (https://www.youtube.com/watch?v=PASeTVPod5U)
Know anyone who might be up for the challenge? ;D
Thanks,
Lloyd
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And I realize that 2162 is too high of a velocity for lead bullets (supposedly) because the rifling will strip off the bullet, ...
That depends on the alloy used and a few other things.
I have shot cast lead at 2600 fps in a 30-06 without issues.
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And I realize that 2162 is too high of a velocity for lead bullets (supposedly) because the rifling will strip off the bullet, ...
That depends on the alloy used and a few other things.
I have shot cast lead at 2600 fps in a 30-06 without issues.
You can also coat the bullets with HighTek coating. It works in powder burners with the hot gas and you need no gas check and no lube in the lube grooves. I use it on my personal slugs to prevent leading and I have to clean my barrel a lot less. Would work great if it evolves where these higher velocities are a reality.
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And I realize that 2162 is too high of a velocity for lead bullets (supposedly) because the rifling will strip off the bullet, ...
That depends on the alloy used and a few other things.
I have shot cast lead at 2600 fps in a 30-06 without issues.
John,
Thanks for letting me know. You hear so many conflicting stories, it is always a pleasure to hear from someone who as actually "done it."
Lloyd
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And I realize that 2162 is too high of a velocity for lead bullets (supposedly) because the rifling will strip off the bullet, ...
That depends on the alloy used and a few other things.
I have shot cast lead at 2600 fps in a 30-06 without issues.
You can also coat the bullets with HighTek coating. It works in powder burners with the hot gas and you need no gas check and no lube in the lube grooves. I use it on my personal slugs to prevent leading and I have to clean my barrel a lot less. Would work great if it evolves where these higher velocities are a reality.
Nick,
Very good! Thanks for helping to kill the myth that non-jacked bullets won't work at high velocity.
Lloyd
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And I realize that 2162 is too high of a velocity for lead bullets (supposedly) because the rifling will strip off the bullet, ...
That depends on the alloy used and a few other things.
I have shot cast lead at 2600 fps in a 30-06 without issues.
John,
Thanks for letting me know. You hear so many conflicting stories, it is always a pleasure to hear from someone who as actually "done it."
Lloyd
You do have to be careful because you can easily lead the barrel if your alloy, lube or sizing is off.
I never tried the coatings.
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With respect to lead bullets and operational velocities. The problem with pure lead is that it strips into the rifling at velocities over about 1500 fps. The earlier solution to that was paper patching or pillow ticking or leather patching with lead balls. That gets the pure lead bullet to about 1750 or 1800 fps where air pressure alone starts to flatten the ball as it travels down range thus decreasing the accuracy. The next step in the evolution of lead projectiles was adding a bit of tin. The amount depended upon how hard you wanted the bullet and that depended upon what velocity you were trying to push the bullet. I've never handloaded with tinned lead but my grandfather and uncles loaded their 30-30 rifles with it and generally shot around 2400 fps. So full power deer loads are certainly possible in lead bullets which have a bit of tin added. I think they were using 5% tin. Don't hold me to that.
You might consider machining a pellet out of Delrin for your experiments. Should be lighter than aluminum by a pretty wide margin.
https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=delrin (https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=delrin)
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OK, from what I am hearing, high velocity lead bullets are all about knowing the tricks, either by trial and error, or hopefully, by getting help from someone who is willing to share the tricks that they have learned.
Thanks,
Lloyd
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OK, from what I am hearing, high velocity lead bullets are all about knowing the tricks, either by trial and error, or hopefully, by getting help from someone who is willing to share the tricks that they have learned.
Thanks,
Lloyd
Here is a technical discussion by someone who knows far more about it than me. http://www.lasc.us/Fryxell_Book_Chapter_3_alloySelectionMetallurgy.htm (http://www.lasc.us/Fryxell_Book_Chapter_3_alloySelectionMetallurgy.htm)
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No rifling = no leading.... so I don't think Lloyd has to worry.... especially with his aluminum pellets.... *grin*....
WELL DONE LLOYD !!! .... Next stop, Mach 2.... ;D :o 8)
Bob
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No rifling = no leading.... so I don't think Lloyd has to worry.... especially with his aluminum pellets.... *grin*....
WELL DONE LLOYD !!! .... Next stop, Mach 2.... ;D :o 8)
Bob
I guess we got off topic a bit, sorry. I still think a Delrin pellet would weigh about half the aluminum one and take the pressure.
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Yes, the Delrin pellet would be great, but unfortunately, the pellet is a structural element in the set-up, held from the rear, and the o-ring actually pulls the pellet from the front. I tried the Delrin initially and it pulled apart. The lightest projectile in the .278 cal so far has been 6.1 gns, but I need to go quite a bit lighter to get more velocity. More design work to do.
Lloyd
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WOW!!!!!!!!!!
Michael, I plan on bringing this to the FunShoot in May. I am looking for someone to catch the bullets, kind of along the lines of the guy in this video :o
https://www.youtube.com/watch?v=PASeTVPod5U (https://www.youtube.com/watch?v=PASeTVPod5U)
Know anyone who might be up for the challenge? ;D
Thanks,
Lloyd
hrmmm dunno about catching..... could try this though...
https://www.youtube.com/watch?v=ppe4O1H4tIw (https://www.youtube.com/watch?v=ppe4O1H4tIw)
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Yes, the Delrin pellet would be great, but unfortunately, the pellet is a structural element in the set-up, held from the rear, and the o-ring actually pulls the pellet from the front. I tried the Delrin initially and it pulled apart. The lightest projectile in the .278 cal so far has been 6.1 gns, but I need to go quite a bit lighter to get more velocity. More design work to do.
Lloyd
Um sorry. Pellet is structural. Maybe you could change that a bit but I get it. It is hard.
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WOW!!!!!!!!!!
Michael, I plan on bringing this to the FunShoot in May. I am looking for someone to catch the bullets, kind of along the lines of the guy in this video :o
https://www.youtube.com/watch?v=PASeTVPod5U (https://www.youtube.com/watch?v=PASeTVPod5U)
Know anyone who might be up for the challenge? ;D
Thanks,
Lloyd
hrmmm dunno about catching..... could try this though...
https://www.youtube.com/watch?v=ppe4O1H4tIw (https://www.youtube.com/watch?v=ppe4O1H4tIw)
Yowww! That guy is serious business.
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... The next step in the evolution of lead projectiles was adding a bit of tin. The amount depended upon how hard you wanted the bullet and that depended upon what velocity you were trying to push the bullet. ...
We (my Dad and I) used an alloy of lead, tin, antimony, and a little copper - the copper was due to how we recovered and recycled the lead. It was a hard alloy with a mirror smooth cast finish. We never measured the Brinell number so I cannot say how hard it was but I would guess around 15 (pure lead is around 5, 3% tin (30:1) alloy is around 9).
My practice load was 165gr @ 2400 fps out of my Model 70 30-06 - and we would push it to 2600 fps occasionally without issues.
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Yes, the Delrin pellet would be great, but unfortunately, the pellet is a structural element in the set-up, held from the rear, and the o-ring actually pulls the pellet from the front. I tried the Delrin initially and it pulled apart. The lightest projectile in the .278 cal so far has been 6.1 gns, but I need to go quite a bit lighter to get more velocity. More design work to do.
Lloyd
Um sorry. Pellet is structural. Maybe you could change that a bit but I get it. It is hard.
You got me to rummaging around in my "plastic materials". I normally keep everything well marked with exactly what material it is, but I did find a piece of unidentified composite that I think is G9 or G10 Garolite. If it is, it has about 3 times the tensile and compression strength of Delrin, and the calcs show that it has the strength needed for the task. It is 60% of the weight of aluminum, so the potential for even higher velocities is very good.
So even though the Delrin didn't work out, you got me to thinking, and sometimes that does the trick.
Lloyd
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Very impressive brother!
And mach 2 is 2250.66 fps by the way. So close! YOU CAN DO IT!
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Yowww! That guy is serious business.
Isao Machii is a Superhuman........ should search a bunch of his other stuff.... he does far more impressive things as well.....
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Hi Lloyd.
I'm new to the GTA. I signed up because of your video that showed that those phenomenal velocities with air power were possible.
I was fascinated when I saw the drawing of your custom breach which was tapered (funnel like) toward the barrel chamber. I don't have any way to prove it, just this instinct that tells me it is important. Besides you wouldn't have built it that way unless you thought it was the way to go.
--Ed.
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Hi Lloyd.
I'm new to the GTA. I signed up because of your video that showed that those phenomenal velocities with air power were possible.
I was fascinated when I saw the drawing of your custom breach which was tapered (funnel like) toward the barrel chamber. I don't have any way to prove it, just this instinct that tells me it is important. Besides you wouldn't have built it that way unless you thought it was the way to go.
--Ed.
Ed,
Glad to have you as a new member in the GTA. Lots of good stuff here, no matter what your air interest or skill level.
Thanks for joing,
Lloyd
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Thank you Lloyd,
Could you explain to me and other members why incorporated this cone shaped breach chamber?
--Ed.
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Thank you Lloyd,
Could you explain to me and other members why incorporated this cone shaped breach chamber?
--Ed.
Ed, sure thing... intuition. The single goal for this setup was to achieve as high a projectile velocity as possible. The conical funnel feeding directly into the back of the projectile seemed to be the most logical way to get the maximum usable airflow into the barrel. There have been discussions of other shapes, convergent-divergent cones to increase velocity, but I am not sold on those. In an open system they can achieve higher flow velocity, but in a closed system maybe not. Harder to make, too, especially for something that might not add any benefit. A parabolic shape might yield slightly higher flow in this case, but that would be hard to prove without a side by side test, which was not the goal. Someone else can do that.
Lloyd
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Next step could be to have vacuum in the barrel...
https://www.youtube.com/watch?v=YYNCGZCul1Q (https://www.youtube.com/watch?v=YYNCGZCul1Q)
4500 psi burst discs.... just thinking.. 8)
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We keep hearing about the vacuum in the barrel idea.... works great for ping-pong balls which are large in area and are being driven by very low pressure, where removing the 14.7 psi in front of the ball is the same as adding the same pressure behind it.... With what we are doing, adding 14.7 psi to 4500 is hardly worth the effort....Would you get a bit more velocity?.... yes but not in proportion to the amount of work involved, IMO.... I have heard Lloyd express the same opinion....
Bob
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Yes, the Delrin pellet would be great, but unfortunately, the pellet is a structural element in the set-up, held from the rear, and the o-ring actually pulls the pellet from the front. I tried the Delrin initially and it pulled apart. The lightest projectile in the .278 cal so far has been 6.1 gns, but I need to go quite a bit lighter to get more velocity. More design work to do.
Lloyd
Um sorry. Pellet is structural. Maybe you could change that a bit but I get it. It is hard.
You got me to rummaging around in my "plastic materials". I normally keep everything well marked with exactly what material it is, but I did find a piece of unidentified composite that I think is G9 or G10 Garolite. If it is, it has about 3 times the tensile and compression strength of Delrin, and the calcs show that it has the strength needed for the task. It is 60% of the weight of aluminum, so the potential for even higher velocities is very good.
So even though the Delrin didn't work out, you got me to thinking, and sometimes that does the trick.
Lloyd
Glad to have poked your noodle. ;D What about carbon fiber? I am not an ME so excuse my dumb questions.
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Just wanted to add my thanks for a fascinating read. I have never heard of anyone using the projectile as the exhaust valve. A greater part of the velocity must be down to the extremely high pressure and long smoothbore barrel. Using the projectile as a dump valve does limit the velocity the system is capable of, especially when using 4500 psi but there is no way around that. An efficient non-dumping straight line valve would be the way to go for beating your current already splendid velocity achievement. That is just my opinion ;D.
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My post was not meant to offend anyone in any way. I did add an expression at the end to the effect that I wasn't trying to teach anyone something they are already aware of but it did not appear ;D.
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My post was not meant to offend anyone in any way. I did add an expression at the end to the effect that I wasn't trying to teach anyone something they are already aware of but it did not appear ;D.
John,
Definitely no concern whatsoever, constructive ideas are always welcome, whether or not they are acted upon. ;) As you know ideas that very good can often be extremely difficult to implement.
For a shot where maximum velocity is the goal, I don't understand how using a non-dumping valve could achieve higher velocities, given the same cc reservoir. However, if you mean using a larger reservoir, metered with a valve such that the exhaust pressure would remain constant, I agree. But I have always found that closing the valve in a precisely timed manner is much more difficult than opening it.
Lloyd
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My post was not meant to offend anyone in any way. I did add an expression at the end to the effect that I wasn't trying to teach anyone something they are already aware of but it did not appear ;D.
John,
Definitely no concern whatsoever, constructive ideas are always welcome, whether or not they are acted upon. ;) As you know ideas that very good can often be extremely difficult to implement.
For a shot where maximum velocity is the goal, I don't understand how using a non-dumping valve could achieve higher velocities, given the same cc reservoir. However, if you mean using a larger reservoir, metered with a valve such that the exhaust pressure would remain constant, I agree. But I have always found that closing the valve in a precisely timed manner is much more difficult than opening it.
Lloyd
I meant using the same size reservoir, pressure etc but with a valve that closes after releasing part of the contents of reservoir. The closed valve has an effect. Give it a try you could be surprised. Be adventurous my friend ;D
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My post was not meant to offend anyone in any way. I did add an expression at the end to the effect that I wasn't trying to teach anyone something they are already aware of but it did not appear ;D.
John,
Definitely no concern whatsoever, constructive ideas are always welcome, whether or not they are acted upon. ;) As you know ideas that very good can often be extremely difficult to implement.
For a shot where maximum velocity is the goal, I don't understand how using a non-dumping valve could achieve higher velocities, given the same cc reservoir. However, if you mean using a larger reservoir, metered with a valve such that the exhaust pressure would remain constant, I agree. But I have always found that closing the valve in a precisely timed manner is much more difficult than opening it.
Lloyd
I meant using the same size reservoir, pressure etc but with a valve that closes after releasing part of the contents of reservoir. The closed valve has an effect. Give it a try you could be surprised. Be adventurous my friend ;D
John,
If you have an appropriate valve, and data to show that what you are suggesting is true at these performance levels, please be so kind as to share it.
Lloyd
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We keep hearing about the vacuum in the barrel idea.... works great for ping-pong balls which are large in area and are being driven by very low pressure, where removing the 14.7 psi in front of the ball is the same as adding the same pressure behind it.... With what we are doing, adding 14.7 psi to 4500 is hardly worth the effort....Would you get a bit more velocity?.... yes but not in proportion to the amount of work involved, IMO.... I have heard Lloyd express the same opinion....
Bob
I'm not so sure that the atmospheric air pressure is relatively insignificant. It certainly is at the beginning where the velocity is well below mach 0.8 for the air in front. However, when that threshold is reached, the gas in front becomes a semi compressible fluid that has no where to go except directly ahead. The pressure at the nose then becomes, I think, significant.
Modeling the air pressure in front of the pellet/bullet is just as problematic as it is behind. You have some that is escaping out the muzzle into a large (~infinite) reservoir, but some is still trapped in the barrel. In the case of an infinitely long barrel, the gas cannot escape. Thus there would be some point at which the pressure in front (plus friction) equals the pressure in the rear. Here, the peak velocity may be before this occurs, and then drops off to a steady state.
Now, if one can get a bunch of consistent shots, then put a thin cap over the muzzle with a vacuum hose fitting, the effect of the atmospheric air pressure could be measured at discrete points when the barrel is shortened incrementally.
In my collection of stuff, I have a .38 i.d. by .625 o.d. length of DOM tubing, with which I am considering instrumenting, and make a similar dump design gun. (The tubing will be used later for a scale version of my howitzer idea.) I have not yet found all the equipment needed that is within my budget. (Multi-channel A/D converters that can handle the speed and simultaneous measurements are kind of pricey. :o) Also, I do not have the means to get pressures much above 3000 psi.
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I agree that the effect would definitely be more than just 14.7 psi.... and once the bullet exceeds 1650 fps (in fact once it exceeds Mach 0.8 ) the air in the barrel will be compressing.... However, even if no air escaped from the barrel, with the 46" barrel we are using, the pressure would only be 10 bar (145 psi) when the bullet is only 4.6" from the muzzle.... which is less than 7% of the residual pressure still driving the pellet at that point.... Most of the acceleration of the bullet occurs in the first half of the barrel or less (in Lloyd's 2162 fps shot, the spreadsheet says it is going 2000 fps at 26" down the barrel).... If the barrel was corked, the average pressure inside at that point would be less than 34 psi at that point (2 lbs. bore drag).... I realize that there would be a pressure gradient, but also, much of the air would have already exited the muzzle, so perhaps such a simple assessment isn't that far off....
As I said, pulling a vacuum would make a difference.... but nowhere near of the magnitude it makes with ping pong ball cannons that operate at low pressures....
Bob
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But you would be consuming energy to compress and accellerate the air molecules in the barrel. Energy that should have been used for accellerating the pellet.
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100% correct.... It is equivalent to overcoming additional barrel friction, as I explained above.... Here is yet another way of looking at it.... There is 2.8 CI of air inside the barrel.... At STP, air is 1.204 kg/m^3, so that air weighs....
2.8 CI of air is 0.000046 m^3, so it would weigh 0.000046 x 1.204 = 0.000055 kg. or 0.85 grains.... In Lloyd's 2162 fps shot, the pellet weighed 7.7 grains, so if we add that to the weight of the pellet (therefore assuming that not even one molecule of air was pushed out the muzzle before compression of the air commenced, which is not the case).... we now have a pellet weight of 8.55 grains....
If we substitute a pellet of 8.55 grains for the one that was 7.7 grains, in Lloyd's J4 Spreadsheet, the predicted velocity drops from 2162 fps to 2127 fps.... Therefore that would be the maximum loss in velocity from the mass of air in the barrel.... less than 2%....
By comparison, in a ping pong ball cannon, if the barrel is only 2 metres long (they are usually much more), the air in the barrel weighs MORE than the ping pong ball.... and the 14.7 psi atmospheric pressure is a MUCH larger percentage of the driving pressure (one I saw was 300 psi)....
Bob
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My post was not meant to offend anyone in any way. I did add an expression at the end to the effect that I wasn't trying to teach anyone something they are already aware of but it did not appear ;D.
John,
Definitely no concern whatsoever, constructive ideas are always welcome, whether or not they are acted upon. ;) As you know ideas that very good can often be extremely difficult to implement.
For a shot where maximum velocity is the goal, I don't understand how using a non-dumping valve could achieve higher velocities, given the same cc reservoir. However, if you mean using a larger reservoir, metered with a valve such that the exhaust pressure would remain constant, I agree. But I have always found that closing the valve in a precisely timed manner is much more difficult than opening it.
Lloyd
I meant using the same size reservoir, pressure etc but with a valve that closes after releasing part of the contents of reservoir. The closed valve has an effect. Give it a try you could be surprised. Be adventurous my friend ;D
John,
If you have an appropriate valve, and data to show that what you are suggesting is true at these performance levels, please be so kind as to share it.
Lloyd
I will see what I can do Lloyd. I don't know about at your performance levels though ;D.
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I am part way to giving you some data Lloyd. A quick update. In amongst my junk I have an old pistol that should provide a base for some figures. It is running at just below 6 ft/lbs energy with a 7" barrel and gives a shed full of shots. The internal valve control device was adjusted for maximum release and a 28" barrel fixed, from an rimfire match rifle. As it was a pistol the reservoir is small. Internally just over 3/4" diameter x 1 3/4". My maths are not good enough for me to work out the capacity allowing for the valve and control device. Fill pressure was 200 bars as I only had 220 left in the tank. Using JSB 15.89 grain pellets 3 shots were fired before refilling. I repeated the exercise several times and the figures were approx. the same each time. 1164 fps, 1171 fps, 1161 fps. Next step is to remove the controlling device to convert it to a dump valve. I will let you know if velocity goes up or down.
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pneumero uno,
Very good. I am glad to see that the experiment is progressing. The 3/4 x 1-3/4 volume calculates out to 12.7cc. You filled to chamber to 200 bar, but do you have a guess as to what the pressure was after the 3rd shot?
Thanks,
Lloyd
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pneumero uno,
Very good. I am glad to see that the experiment is progressing. The 3/4 x 1-3/4 volume calculates out to 12.7cc. You filled to chamber to 200 bar, but do you have a guess as to what the pressure was after the 3rd shot?
Thanks,
Lloyd
I have just tried it before taking out the control device. It is difficult to slowly open the valve when refilling. It jumps to about 100 bars. Filling to 140 bars gives 1165 fps and 110 bars 1135 fps if that helps.
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pneumero uno,
If you start shooting at 220 bar (3190 psi) and finish at 100 bar (1450psi) and get 3 shots 15.89 gn averaging 1165 fps, that gives an air efficiency of about 1.6 fpe/cuin. That is very good. Here is the calculator, but you have to convert the pressure to psi
http://calc.sikes.us/1/index.php (http://calc.sikes.us/1/index.php)
The 1135fps at 110 bar is also very nice!
Lloyd
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Am I the only one who thinks our airgun community should proceed with caution before implementing This further?
Otherwise the government will restrict air rifles even more.
But congrats and thanks for pushing the envelope!
^^^YES!
air guns are NOT considered as being firearms in California (yet) but...they do have a generic term to cover things they deem as being 'unacceptable: "Destructive device"
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Am I the only one who thinks our airgun community should proceed with caution before implementing This further?
Otherwise the government will restrict air rifles even more.
But congrats and thanks for pushing the envelope!
^^^YES!
air guns are NOT considered as being firearms in California (yet) but...they do have a generic term to cover things they deem as being 'unacceptable: "Destructive device"
dwalk,
Please go back and read my reply # 16 to the post you quoted. I certainly respect your and Tuckeron's thoughts on that particular subject, and I know you are not alone, but that is not what this thread is about.
Thank you,
Lloyd
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pneumero uno,
If you start shooting at 220 bar (3190 psi) and finish at 100 bar (1450psi) and get 3 shots 15.89 gn averaging 1165 fps, that gives an air efficiency of about 1.6 fpe/cuin. That is very good. Here is the calculator, but you have to convert the pressure to psi
The 1135fps at 110 bar is also very nice!
Lloyd
That was certainly quite a blast ;D. I was wrong. The fill pressure is 200 bar. I removed the internal controlling device so that all the air was dumped on one shot. The volume was slightly increased as a result. Velocity was 1363 fps with 15.89 JSBs.
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pneumero uno,
If you start shooting at 220 bar (3190 psi) and finish at 100 bar (1450psi) and get 3 shots 15.89 gn averaging 1165 fps, that gives an air efficiency of about 1.6 fpe/cuin. That is very good. Here is the calculator, but you have to convert the pressure to psi
The 1135fps at 110 bar is also very nice!
Lloyd
That was certainly quite a blast ;D. I was wrong. The fill pressure is 200 bar. I removed the internal controlling device so that all the air was dumped on one shot. The volume was slightly increased as a result. Velocity was 1363 fps with 15.89 JSBs.
That is one fast JSB! ;D
Lloyd
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Thats a nice one Loyd, can't believe I have missed this thread. That is quite clever on holding the pellet and not using a valve.
I shot some 8gr plastic sabots out of my 357 with helium and we clocked them around 845m/s at the muzzle. Just to see how fast they can fly. Have a pic of the a chrony session somewhere hafto try and find it.
I do like these experiment threads, keep them coming.
Marko
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pneumero uno,
If you start shooting at 220 bar (3190 psi) and finish at 100 bar (1450psi) and get 3 shots 15.89 gn averaging 1165 fps, that gives an air efficiency of about 1.6 fpe/cuin. That is very good. Here is the calculator, but you have to convert the pressure to psi
The 1135fps at 110 bar is also very nice!
Lloyd
That was certainly quite a blast ;D. I was wrong. The fill pressure is 200 bar. I removed the internal controlling device so that all the air was dumped on one shot. The volume was slightly increased as a result. Velocity was 1363 fps with 15.89 JSBs.
That is one fast JSB! ;D
Lloyd
Thank you Lloyd but I don't think it would have the usual JSB accuracy ;D. Rather unpleasant with all the blast too. Nowhere near your outstanding achievements but as you know it was done to prove a point, and failed ;D. The experiment with the controlling device was done at 200 bar not 220 as that was the dive bottle pressure so the test could be repeated. It uses little air. Will have to get a 300 bar tank :(
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Thats a nice one Loyd, can't believe I have missed this thread. That is quite clever on holding the pellet and not using a valve.
I shot some 8gr plastic sabots out of my 357 with helium and we clocked them around 845m/s at the muzzle. Just to see how fast they can fly. Have a pic of the a chrony session somewhere hafto try and find it.
I do like these experiment threads, keep them coming.
Marko
Some folks might say that these posts that built around totally impractical devices are pointless. But there is always something new to learn.
Lloyd
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If any of you have a powerful .25 cal PCP, something about 100 FPE or more, and want to try exceeding 1650 fps yourself, check out Reply #490 in this thread...
http://www.gatewaytoairguns.org/GTA/index.php?topic=102604.480 (http://www.gatewaytoairguns.org/GTA/index.php?topic=102604.480)
I used my .25 cal Disco, tethered at 2900 psi, to drive a tinfoil wrapped airsoft BB at over 1750 fps.... with NO changes to the gun.... :o
Bob