GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: lloyd-ss on August 17, 2011, 08:47:42 AM
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Tworr's thread about his new 308 Condor stirred up a lot of interest in calculating air usage efficiency numbers for PCPs, and in particular, for big bores.
Air efficiency is a calculation of how much air a gun uses to produce a certain amount of energy (FPE). It is commonly measured two ways:
FPE/cuin the number of foot pounds of energy that can be produced per cubic inch of air at standard sea level pressure
bar-cc/FPE number of ccs of air at sea level pressure that it will take to produce one foot pound of energy
Both calculations convert the amount of compressed air at any given pressure back to a level playing field of sea level pressure. Basically, how big a volume does that burst of air that comes out behind the pellet expand into? You might think of it as putting a plastic bag on the end of the barrel and seeing how big it blows up. One is the inverse of the other, with the conversion of cc's to cubic inches thrown in. For FPE/cuin, a larger number is more efficient, and for bar-cc/FPE, a smaller number is better.
For example, a fairly efficient gun like a Disco might produce 2 FPE/cuin, which is the same as it using 8.19 bar-cc/FPE. So, if that Disco produces a 20FPE shot, it will puff that plastic bag up to 10 cuin. But if its efficiency were only 1 FPE/cuin, it would puff the bag up to 20 cu in. And if you had a big bore that produced 200 FPE at a 1 FPE/cuin rate, it would puff that bag up to 200 cuin.
Has anyone seen an online calculator for this, or would you like to have one available? I think I can get one up and running in a short while (or a little longer, seeing I have to talk my wife into doing the web programming part), a fairly simple one first, then one with more capability.
Bob added some mods to my initial suggestions of calculator inputs and outputs, but then he got carried away and got greedy, LOL. That's ok Bob, all ideas are welcome! Bob, you can add your other embellishments back in if you want. ;D
Lloyd
PS, I hope my explanations were clear and accurate. :-\
Here is what Bob has suggested, which could be a good starting point:
I would suggest entering the average velocity (the Chrony gives you that) instead of the average energy and let the program do the math....
Inputs:
1. Pressure before first shot
2. Pressure after the last shot
3. Tank volume (cc)
4. Pellet weight (grains)
4. Number of shots
5. Average velocity for all shots taken.
Outputs:
1. Tank Volume (CI)
2. Average energy in FPE
3. Efficiency in bar-cc/FPE
4. Efficiency in FPE/cuin
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HI Lloyd....
This is a GREAT idea, and the way you have it currently set up is fine.... I know I was being a bit silly with the Metric to Imperial stuff.... Everybody on this website seems to work with the Imperial units, except that the reservoirs on the guns are mostly rated in cc.... so lets just stick with those units.... Pressure should be in psi instead of bar, and velocity should be in fps instead of m/s.... but I think that's what you had in mind anyway.... If somebody has different units, they can easily convert before inputting the numbers....
Bob
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Can you include cf in the tank in put ? What about psi per shot average ? Marvin
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Can you include cf in the tank in put ?
Not sure what you mean by that.... The reservoir volume where you are reading the pressure drop is what is needed.... If the gun is tethered to a SCUBA tank then you would use the internal (water) volume of the tank in cc (not the CF content) and the pressure drop for the string....
What about psi per shot average ?
That could be included as an output, but it isn't a linear function.... The psi drop starts off less and increases in a non-regulated PCP.... In a regulated gun it should be linear, however.... I think including it as an output would be OK though, as long as you realize the limitations of the information....
Bob
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There are online tools that allow you to build a excel spreadsheet on the web and people can enter their own data.
This isn't just saving the data to post as a html file, but actually a working database. I had found a free one yesterday, but I'm looking for it again.
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If I am reading this right none of this is liner. It is a average over a said amount of shots . Yes it is under stood . Then can a conversion from cf to cc be listed ? Marvin
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1 CF = 1728 CI = 28,317 cc.... However, I don't think that's what you mean.... You would be unlikely to use 1500 psi from a tank with an internal volume of even 1 CF as that would be 103 CF = 178,759 CI = 2,929,329 cc of air used....
SCUBA and SCBA tanks are rated in CF because that is the amount of air they hold at their rated pressure.... As an example, a 3000 psi tank rated at 80 CF holds that much air at 1 bar.... Its internal (water) volume is NOT 80 CF.... Just think how big that is!.... A tank 4' x 4' x 5' inside would have a volume of 80 CF.... The internal volume of the tank depends on the rated pressure....
For an 80 CF, 3000 psi SCUBA tank, the internal volume would be 80 / (3000 / 14.5) = 80 / 207 = 0.386 CF.... That would be 668 CI or 10,944 cc.... However, an 88 CF SCBA tank (which contains more air) is actually smaller inside because it contains 88 CF when filled to 4500 psi.... The internal volume would be 88 / (4500 / 14.5) = 88 / 310 = 0.284 CF.... That would be 491 CI or 8038 cc....
What we need for the input for the calculator is EITHER the inside (water) volume of the reservoir and the pressure drop during the shot string.... OR the actual amount of air used at 1 bar pressure.... Since we don't have a flow meter that will measure how many CF have been used up, the easiest way is to use the volume and pressure.... If you are using a tethered setup, you would need to calculate the internal volume (in cc) of the tank (as shown above) and use that as the reservoir size.... If you do this for each tank you have and write it down on the tank, you can then use that for your input volume.... For best results, you would have to add the volume of the reservoir on the gun (if any) to the tank volume....
Note that small (paintball) tanks are rated in CI and that is the actual internal (water) volume of the tank so no conversion is necessary other than to multiply by 16.4 to convert to cc....
HTHs....
Bob
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http://www.trirand.com/blog/ (http://www.trirand.com/blog/)
https://github.com/mleibman/SlickGrid/wiki (https://github.com/mleibman/SlickGrid/wiki)
http://www.labnol.org/software/embed-tables-spreadsheet-data-in-websites/7435/ (http://www.labnol.org/software/embed-tables-spreadsheet-data-in-websites/7435/)
Maybe one of these will help in some way.
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Bob please . I think you know what is needed to do the job of a tethered rifle . Can it be done .Marvin
(http://i301.photobucket.com/albums/nn55/melloroadman/001A-1.jpg)
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The best way is for you to calculate the internal volume of your tank.... I can help if you give me the CF and pressure rating.... Then you use that as the volume input for the calculator....
Personally, I would think that the pressure drop on a large tank (I assume you are talking an 80 CF SCUBA tank) would be so difficult to read for a single shot string that it would be almost impossible to get any accuracy.... Let's take a string from your Corsair as an example.... The reservoir is only 155 cc, and you used (as an example) 2000 psi for a shot string.... If you had the gun directly tethered to an 80 CF SCUBA tank (which is 10,994 cc) the pressure drop for the same string would only be 2000 x (155/10,994) = 28 psi.... Can you read the gauge on your SCUBA tank accurately to within 1 psi?.... 3 psi?.... An reading error of only 3 psi in opposite directions at each end of the string on the SCUBA tank would be 20% of the results of the efficiency calculator.... Most 3500 psi gauges I have seen only hae 100 psi divisions.... Anything less than that is an estimate.... I can only read such a gauge to ~50 psi....
I'm not trying to be an ^&* here.... perhaps Lloyd can help explain....
Bob
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OK now that you added the diagram I understand what you are trying to do.... and yes, you can do it that way for very large shot strings with a very powerful gun.... I would suggest that the simpler way (that would work for any size gun, tethered or not) would be to use the volume of your tank (668 CI) and the pressure drop (400 psi) in the calculator.... The results would be:
400 psi / 14.5 = 27.6 Bar x 668 CI = 18,428 CI / 1728 = 10.66 CF of air used....
Lloyd can chime in if he thinks there is a practical way to allow the CF of the tank (and the rated pressure) to be input.... and yet not REQUIRE that is the way the input is done as then it would be useless for short strings with a less powerful gun....
Bob
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http://www.trirand.com/blog/ (http://www.trirand.com/blog/)
https://github.com/mleibman/SlickGrid/wiki (https://github.com/mleibman/SlickGrid/wiki)
http://www.labnol.org/software/embed-tables-spreadsheet-data-in-websites/7435/ (http://www.labnol.org/software/embed-tables-spreadsheet-data-in-websites/7435/)
Maybe one of these will help in some way.
Todd,
I will take a look at some of those and see how they might work. Getting a database of statistics going would be very neat. I just hope it wouldn't turn us all into a bunch of liars, like fisherman! Or gas mileage! ;D
The first one will be a pretty straight forward web-based calculator that anyone can use. In the future it can get more involved, for sure.
Lloyd
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Bob please understand that a shot string would not consist of 3-5 shots . It is more in line with what you see . I understand what you are saying and that is why the shot string is as well increased . One could as well start with 3000 psi and shoot till the psi is at 2950 and calculate that way as well with the number of shots taken .
My tank sizes are 80 cf 2 are rated at 3300psi and 1 at 3000 psi .All 3 have the same out side measurements . But others may want to use this program as well .I am not the only one that tethers Marvin
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The problem with only using 50 psi for a string is are you really using 50 psi, or only 45?.... or 55?.... or 60?.... The difference works out to a HUGE percentage error and makes the whole point of doing an efficiency calculation pretty much useless.... Unless you are shooting tethered, most shot strings ARE 5 or 10 or 20 or 40 shots, not 120.... There is nothing wrong with shooting 120 shots or more when tethered, and in fact the advantage to it is that you have enough gauge movement to be able to get reasonably accurate results....
While your three 80 CF tanks may be the same dimensions on the outside, they will be different inside.... The 3300 psi tanks would be 80 / (3300 / 14.5) = 80 / 228 = 0.351 CF = 606 CI = 9,936 cc.... All you need to do is write 10,994 on the outside of your 3000 psi tank, and 9,936 on the outside of your 3300 psi tanks and you can use the calculator the same as someone shooting 10 shots through a Disco.... This calculator has to work for everybody to be useful, don't you agree?....
Perhaps a small calculator to change the CF and rated pressure of a SCUBA/SCBA tank into volume in cc which could then be used in the main calculator would be useful?....
Bob
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..........................
Lloyd can chime in if he thinks there is a practical way to allow the CF of the tank (and the rated pressure) to be input.... and yet not REQUIRE that is the way the input is done as then it would be useless for short strings with a less powerful gun....
Bob
Bob and Marvin,
First, let's talk about the basic calculator which would be where you entered the cc volume of the tank on the gun and shot it un-tethered. That will probably be the most accurate way to do the calcs, because the pressure changes will be large and errors in reading won't matter much. Marvin, you are right, the air efficiency changes as the pressure in the tanks drops and is not necessarily linear.
If you just shoot one long string, everything will be averaged and it will look linear. One way to get more accurate results if you were, say, shooting a gun from 3500 psi all the way down to 1000 psi, would be to break it into 2 or 3 strings. Lets say after shot six you are at 2550 psi, then shot 12 puts you at 1450, and the shot 17 is 1000psi.
You'd have 3 different shot strings to enter, each with their own average velocity and own beginning and ending psi.
Then the output would show how the fpe and efficiency changed for each different string. It can show where the most efficient fill pressure for a particular pellet might be. Kinda like doing a dyno curve on an engine while monitoring the fuel consumption to find the most fuel efficient speed at that particular load.
Lloyd..... more coming
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I like the idea of breaking the string into sections so you can look at the efficiency in various sections of the curve.... All that is required is to take intermediate pressure readings after every "X" shots and then input each string into the calculator separately.... Like Butcher said, only take 3 shots as the 4th requires a lot more pumping.... The same thing would apply to a Disco.... Instead of shooting 25 shots, just take 10 or 15....
Bob
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Thanks Bob . But as far as reading the gauge . I think that it would be just as accurate if not more so than the guess at the refill psi after the shot string at each refill . A flow meter is the only true means of removing this error . Marvin
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I usually record the pressure after each shot string (I know, I ALWAYS should).... I agree that the usual 1" gauge mounted on a PCP is pretty useless with it's 500 psi divisions.... That is why I usually replace them with a gauge with 100 psi increments.... If that isn't possible, and you have a good gauge on your fill setup you can tell what pressure you are at by filling slowly until you hear the check valve "click".... or with a pump, wherever the gauge stops moving 100-200 psi on a pump....
My point is that it's a lot more accurate even if you are out by 100 psi when you have a 1000-1500 psi range than trying to read a gauge to just a few psi when the difference between start and finish pressures is only 50-100 psi.... When all is said and done, the only REALLY accurate method is the way Lloyd does it.... with a strain gauge and a digital readout.... (lil' jealous look)....
Our methods may vary, and so, therefore, will the accuracy of our results.... In the end, all that matters is if you feel you are getting useful information....
Bob
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Bob please understand that a shot string would not consist of 3-5 shots . It is more in line with what you see . I understand what you are saying and that is why the shot string is as well increased . One could as well start with 3000 psi and shoot till the psi is at 2950 and calculate that way as well with the number of shots taken .
My tank sizes are 80 cf 2 are rated at 3300psi and 1 at 3000 psi .All 3 have the same out side measurements . But others may want to use this program as well .I am not the only one that tethers Marvin
Marvin,
Yup, I see what you mean. Many folks like to tether their guns and shoot a butt load of shots and then want to do some calculations. If you can get an accurate measurement of the drop in tank pressure, good enough!
So if the gun has a 400cc tank, and you have an 80 cuft 4500 psi tank, how many cc's do you add to the 400cc in the gun to get the water volume of the entire set-up? That's really all you need to now, the water volume of each tank. I will add that to the list.
I was looking on the scuba forums and there is certainly a lot of confusion there on tank volumes, too. We are not alone.
Lloyd
P.S. Thanks everyone for chiming in on this.
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I have a digital pressure gauge that i use with my prototypes. If you look back at some of my excel spreadsheets you can see that I have the psi for each shot recorded. I ended up making a gauge from a pressure sensor chip and and an instrument amp and an A to D convertor. It has a resolution of 1 psi, and an accuracy of maybe 3 psi. For me it works great. One drawback is that because darn near everything I build has some sort of slow leak, it is painful to sit there and watch the LCD display slowly tick the numbers off as the air slowly leaks. :-[
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Lloyd .Thank you again . And we all know the fisherman stories will happen . But it will be a useful tool for most . Marvin
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Lloyd, I asked our programmers and they said the easiest way was to use Google Docs and make it available online.
They said that once you get the form ready to let them see it and they could build it java script.
BTW, when this post hits page three, I'm holding this train up and hijacking it!! :P
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Lloyd, I asked our programmers and they said the easiest way was to use Google Docs and make it available online.
They said that once you get the form ready to let them see it and they could build it java script.
BTW, when this post hits page three, I'm holding this train up and hijacking it!! :P
tworr,
Thanks for the warning, I'll be watching my back for suspicious activity! ;)
I've got a php script calculator partially finished right now and will make that available as soon as I get it going.
After that I'll take a look at the google docs. Thanks for the offer on the programming, that might be the direction to go.
Lloyd
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OK folks, here is the link to the calculator.
calc.sikes.us (http://calc.sikes.us)
Just click on it. There is no www in front of it.
Right now the only calculator is for PCP Air Usage Efficiency, but I'll be putting some others up shortly. Bob (rsterne) is the serious statistician on that stuff and taught me a lot about it.
The efficiency calculator basically tells you how much pellet energy you are getting from the air that the gun uses. There are two ways of measuring it:
FPE per cubic inch of air (bigger number is more efficient)
and
bar-cc per FPE (smaller number is more efficient)
They are pretty much the same thing, but one is the inverse of the other with the cc-cuin conversion thrown in.
This calculator can be a tool for working with PCPs.
Bob gave me some ranges that you might expect to see from different types of PCPs:
Loud, overpowered, inefficient.... 0.6 to 0.8 FPE/CI (20-27 Bar-cc/FPE) - (big power at a high air cost, just a few shots per fill)
Powerful, useable efficiency.... 0.8 to 1.1 FPE/CI (15-20 Barcc/FPE) - eg. Modded Disco, MRod, Hatsan
Moderate power, good efficiency.... 1.1 to 1.4 FPE/CI (12-15 Barcc/FPE) - eg. Stock Disco, MRod, Hatsan AT44
Low power, high shot count, excellent efficiency.... 1.4 to 2.0 FPE.CI (8-12 Barcc/FPE)
Enjoy it folks, and let me know if you have questions or suggestions.
Lloyd
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Nice work, Thanks for putting in the time to do this.
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Thanks again . Marvin
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Lloyd I just took a better look at it .Make sure you tell the wife thanks too .Marvin
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Lloyd I just took a better look at it .Make sure you tell the wife thanks too .Marvin
Marvin,
You bet! And thanks for your suggestions, too. I hope folks will find his useful.
Lloyd
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The Calculator works great, Lloyd, and many thanks to your wife as well.... The numbers I gave you are based on the work I've done on .177 to .25 cal PCPs.... I only have very limited data on Bigbores, and only time will tell how they compare to the smaller calibers....
I have so far found that there seems to be a edge in efficiency as the caliber increases in the same (or similar) gun.... ie .25s seem to be slightly more efficient than .22s which have an edge over .177s.... The one 9mm I have built also follows this trend, but when you consider it's quite low powered (2260 based carbine) the extra efficiency could well be because of that.... Even though it's nearly triple the FPE of a Disco, it's pretty tame for a 9mm....
The one obvious difference with Bigbores is that with their huge barrel, they can really eat a lot of air.... From some of the limited data I have seen so far, efficencies can be much less than 0.6 FPE/CI.... More data will enable us to get a much better feel for how Bigbores fit in, efficiency-wise....
Bob
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Some further thoughts about how to compare different calibers.... that might give us a better handle on what to expect.... Let's say we establish a "baseline" FPE relative to the caliber.... How can we do that?.... Well I'll throw out this idea.... Let's take the weight of a bore-sized lead ball and fire it at 950 fps.... Why that speed?.... Well, it's about as fast as is reasonable to stay out of the transonic region.... In addition, it makes it REALLY easy to figure out the FPE.... it's twice the weight of the ball.... Here are the weights and FPE for the various calibers....
.177 - 8.3 gr. - 17 FPE
.20 - 12.0 gr. - 24 FPE
.22 - 15.3 gr. - 31 FPE
.25 - 23.4 gr. - 47 FPE
.30 - 43.8 gr. - 88 FPE
.35 - 67.8 gr. - 135 FPE
.41 - 103 gr. - 207 FPE
.45 - 143 gr. - 286 FPE
.50 - 182 gr. - 364 FPE
.58 - 292 gr. - 585 FPE
OK, bear with me for a minute.... Look at the .22 cal at 31 FPE and the .25 cal at 47 FPE.... Those are pretty healthy numbers, and I have evidence of lots of guns that can shoot at that level at an efficiency of right around 1.0 FPE/CI with pellets of about that weight.... It is reasonable to assume that larger calibers should be able to meet that air usage at the power levels given, no?.... So just for the heck of it, let's for a minute consider that to be a "standard gun".... What range of power levels do we realistically have, and what are the efficiency levels for those?....
Let's take a gun half as powerful.... 8 FPE in .177, 15 FPE in .22 cal, 68 FPE in 9mm.... I've tested guns in those power ranges and they tend to be about 1.50 FPE/CI give or take.... How about a gun twice as powerful.... Well, I've done a .22 cal at 52 FPE and it was 0.6 FPE/CI.... so at 62 FPE I'm betting 0.5 FPE/CI might be pretty good going.... See what I'm getting at.... some way to "catagorize" your gun and get some idea of how much air it might use.... Whether or not this will hold true for Bigbores I don't know.... but it will be fun finding out.... ;D
Bob
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Bob,
With the shooting I've done with my bigbores, I have seen the efficiencies run off the charts at both ends. From less than .7 FPE/cuin for a high velocity shot to more than 4 FPE/cuin for a slow moving heavy weight.
It will be interesting to see what reports we get.
Lloyd
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Lloyd I know you have recorded the psi per shot as well . How did they fare with the numbers you mentioned . Marvin
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Lloyd forget that last question . I looked at your test mule charts . When I am tethered and get a psi per shot on the converter you have given us is there a way I personally can convert that over to what the psi per shot average would be to a tank around 300-500 cc as you have done in your charts ? Marvin
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Lloyd forget that last question . I looked at your test mule charts . When I am tethered and get a psi per shot on the converter you have given us is there a way I personally can convert that over to what the psi per shot average would be to a tank around 300-500 cc as you have done in your charts ? Marvin
yes. I will work on that today at lunch and post something.
Lloyd
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Marvin,
I had a chance to work on it:
If you have data from a tethered tank and want to convert it to the guns actual volume, this will give a reasonable estimation.
(tank vol + gun vol) / gun vol = tank ratio
tank ratio x psi used = psi for gun tank only
Example:
1200 cc (water volume) tethered tank, 300cc gun, 12 psi/ shot used
(1200 + 300)/300 = 5
12 psi x 5 = 60 psi with only the gun tank
This is an approximation, and even though the psi for the shot will be different, the efficiency calculation should give the same result. However, tethered tanks do make guns behave differently. A similar calculation technique can be used to approximate what the usage would be if the gun had a larger or smaller tank.
Lloyd
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Lloyd I know you have recorded the psi per shot as well . How did they fare with the numbers you mentioned . Marvin
Marvin,
I think you found that info on the test mule thread. DO notice that I was using different tank volumes for each set. I have filler plugs I put in the tank.
I have to get back on that project and post some more, BTW. ;)
Lloyd
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Lloyd thanks again . Marvin
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the calculator works excellent
thank you marvin and bob
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The thanks goes to Lloyd . Marvin
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Some further thoughts about how to compare different calibers.... that might give us a better handle on what to expect.... Let's say we establish a "baseline" FPE relative to the caliber.... How can we do that?.... Well I'll throw out this idea.... Let's take the weight of a bore-sized lead ball and fire it at 950 fps.... Why that speed?.... Well, it's about as fast as is reasonable to stay out of the transonic region.... In addition, it makes it REALLY easy to figure out the FPE.... it's twice the weight of the ball.... Here are the weights and FPE for the various calibers....
.177 - 8.3 gr. - 17 FPE
.20 - 12.0 gr. - 24 FPE
.22 - 15.3 gr. - 31 FPE
.25 - 23.4 gr. - 47 FPE
.30 - 43.8 gr. - 88 FPE
.35 - 67.8 gr. - 135 FPE
.41 - 103 gr. - 207 FPE
.45 - 143 gr. - 286 FPE
.50 - 182 gr. - 364 FPE
.58 - 292 gr. - 585 FPE
OK, bear with me for a minute.... Look at the .22 cal at 31 FPE and the .25 cal at 47 FPE.... Those are pretty healthy numbers, and I have evidence of lots of guns that can shoot at that level at an efficiency of right around 1.0 FPE/CI with pellets of about that weight.... It is reasonable to assume that larger calibers should be able to meet that air usage at the power levels given, no?.... So just for the heck of it, let's for a minute consider that to be a "standard gun".... What range of power levels do we realistically have, and what are the efficiency levels for those?....
Let's take a gun half as powerful.... 8 FPE in .177, 15 FPE in .22 cal, 68 FPE in 9mm.... I've tested guns in those power ranges and they tend to be about 1.50 FPE/CI give or take.... How about a gun twice as powerful.... Well, I've done a .22 cal at 52 FPE and it was 0.6 FPE/CI.... so at 62 FPE I'm betting 0.5 FPE/CI might be pretty good going.... See what I'm getting at.... some way to "catagorize" your gun and get some idea of how much air it might use.... Whether or not this will hold true for Bigbores I don't know.... but it will be fun finding out.... ;D
Bob
Bob,
I tend to disagree, because this scale is regressive against the larger calibers. Here is why:
As you increase the bore dia, the area of the bore goes up with the square of the increase, but the weight of the ball goes up with the cube. Because the force applied to the bullet is proprtonal to the area of the bore, the increase in force will lag far behind in the larger calibers.
For example, going from the extremes of .177 to .58, the dia goes up by a factor of 3.3, and the bore area goes up by 10.7, but the weight of the bullet goes up by a factor of 35.2. So the .58 caliber is at a 3.3 to one weight disadvantage.
To equalize things you would have to reduce your velocity goal for the larger calibers by dividing the baseline velocity by the square root of the increase in diameter. That would give a more level playing field.
So the target velocities would be
.177 950 fps
.20 893 fps
.22 852
.25 799
.30 729
.35 675
.41 624
.45 595
.50 565
.58 524 fps
That will make the " force density??" on the bottom of the bullet the same in all calibers. That means if the pressures and barrel lengths are equal, so will the velocities.....theoretically.
That might have screwed up what you were trying to accomplish but it does make for a more fair comparison. If you wanted to keep the velocities equal, you would have to drop the weight of the bigbore bullets way back.
Driving the bullets to 950 fps is a lot harder for a big caliber than it is for the little calibers.
Lloyd
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I know exactly what you are saying.... and I agree with everything you are saying IRT the "force density" on the base of the bullet.... However, we have both seen what appears to be big advantages in efficiency in favour of the Bigbores.... for whatever reason.... We know because we have to play with that (efficiency factor) in our calculations.... You have results where you were pushing a 143 gr. roundball in .458 cal at ~950 fps and efficiencies of well over 1.0 FPE/CI.... I was just trying to come up with a "target" set of numbers that is somewhat in agreement with real world results....
As an example, using your velocities.... the .45 cal shooting a 143 gr. roundball at 595 fps is only 112 FPE.... I don't think anyone would consider that to be of the same relative power level as a .25 cal MRod shooting at 47 FPE.... but rather as a "low powered" gun.... However, at 950 fps, it's 286 FPE, which although not a high power level for a .45 cal (the DAQ is 500 FPE+) seems to me to be a relatively easily attainable, and yet signficant power, comparable with that MRod.... That DAQ would then compare to a .25 Condor in relative terms....
The math may not be right.... but because Bigbores are more efficient.... I think the concept is.... I once asked a long time PCP builder what he used as a benchmark for performance, ie his goals.... His reply was "a bore sized roundball at 1100 fps and a bullet of twice that weight at 880 fps"..... I think those are pretty good targets.... The .308 DAQ fires a bullet nearly 3 times roundball weight at 850ish (200+ FPE) .... and the .458 DAQ shoots a bullet of 3 times roundball weight (432 gr.) at 732 fps (500+ FPE).... I'm betting that the Rogue isn't breaking too much of a sweat to hit 135 FPE and will probably deliver over 1.0 FPE/CI doing it....
All I'm doing is trying to come up with a guideline "standard" of performance in a PCP.... that hopefully, with enough data will show relatively similar levels of efficiency across all calibers.... There will always be exceptions to the rules, of course.... and maybe someday we'll understand enough about all the factors that affect efficiency to make sense of it all....
Bob
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Can I ask why is CI used instead of psi as the efficiency standard . Marvin
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Because psi is only half the number you need.... You also need the volume of the container that the pressure is contained in.... The "CI" in the standard is at 1 Bar pressure.... ie normal atmospheric pressure....
If you just used psi, then you would get a different answer for a gun tethered to a SCUBA tank than for the exact same gun on it's own.... It the tank was 10,000 cc and the gun only 100 cc, your pressure drop would be 100 times larger for the gun alone, so if you based the efficiency on that the results would indicate the gun was 100 times as efficient when tethered....
Bob
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I understand what you are saying . But for a tethered rifle the solution has been addressed . So if we take the tethered out of the picture . Why is CI the bench mark ? Marvin
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Marvin,
The cubic inch is one cubic inch of air at 14.5 psi (standard pressure, approx 1 bar), so there is both volume and pressure needed to equalize everything.
If you always shoot out of the same gun with the same tank, it doesn't really matter. If you have a 400 cc tank and it drops 30 psi per shot, and then you put on a 200cc tank, it will drop 60 psi per shot. The bar-cc or cuin at std pressure are just ways to be able to compare apples to oranges.
Lloyd
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........................
All I'm doing is trying to come up with a guideline "standard" of performance in a PCP.... that hopefully, with enough data will show relatively similar levels of efficiency across all calibers.... There will always be exceptions to the rules, of course.... and maybe someday we'll understand enough about all the factors that affect efficiency to make sense of it all....
Bob
Bob, I agree that having some standard way to compare different calibers and guns might be nice. I just think the choice of 950 fps puts the bigger calibers at a disadvantage and none of them will show good eff at 950 fps. It's like trying to dyno a big block chevy at the same RPM as a DOHC honda. They BB Chevy is going to run out of breath.
Testing a big bore at 950fps puts up a couple of obstacles that the small calibers don't have:
You'll need higher air pressure.
You'll be limited to a light weight bullet.
Shooting a light weight bullet is always an eff disadvantage for a big bore.
You will be coming off the edge of the efficiency plateau so a shot at 2500 psi will give a totally different eff than a shot at 3400 psi, even though they might both achieve 950 fps.
My point is that I think you will be trying to get comparable, relevant eff numbers while operating the big bore out of its normal eff range.
IMHO.
Lloyd
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Thank you both . The apple to orange thing helped . For me the calculator will be very useful for finding out info on my individual rifles not comparing big to small so much . Marvin
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ahhhhhhhhhhh I see what you're saying Lloyd.... OK, so just use the FPE numbers (which come from a roundball at 950).... but you could just as easily say that the FPE = twice the weight of a roundball and leave the velocity out of the picture all together.... *grin*....
Are you OK with that?.... Looks like it should be pretty close.... "A PCP operating at an FPE equal to twice the weight of a roundball should have an efficiency of about 1.0 FPE/CI"....
Bob
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ahhhhhhhhhhh I see what you're saying Lloyd.... OK, so just use the FPE numbers (which come from a roundball at 950).... but you could just as easily say that the FPE = twice the weight of a roundball and leave the velocity out of the picture all together.... *grin*....
Are you OK with that?.... Looks like it should be pretty close.... "A PCP operating at an FPE equal to twice the weight of a roundball should have an efficiency of about 1.0 FPE/CI"....
Bob
Ok, that sounds like a good starting point to explore from.
Lloyd
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As this is set up it is a average of air usage over a shot string . Were as Lloyd gives us info on a one shot bases on his mule . Way more equipment than I have . And I am not competing here as well . But if I know that the maximum energy of my rifle is at 3000 psi . I tether it to a tank with a regulator and good gauges that are marked in 100 psi interments . Shoot say 200 shoots and use 100 psi of air . Average out my chrony reading which should all be very close . Use this calculator correctly . I should have a very accurate reading as to what this said rifle does in effency at its top power level correct . Marvin
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Marvin,
Hmm, let me think about this. The regulator changes things.
Lets say you set the reg to 3000 psi and hook it up to the gun so that the gun is pressurized to 3000. You check the gauge on the tethered tank and it is ... say, 3700. Then you shoot your string. The gun is still at 3000, but the tank has dropped to 3600. Then into the calculator for the volume you would put the water volume of just the tethered tank. Starting psi would be 3700, and ending psi would be 3600.
The reason the volume of the gun tank doesn't matter is because it stays at 3000 psi from beginning to end, and doesn't really loose any pressure. The tethered tank looses all the pressure.
But if you were NOT using a regulator then the water volume of the entire set-up would have to be used (tethered tank, gun tank, and hoses).
I think your method will give pretty good results. You could give it a try by putting some guesstimated numbers into the calculator, and then repeat it but change the psi 5 pounds higher or 5 pound lower to simulate a bad reading, and see how much difference it makes in the efficiency number.
Sounds good. ;D
.....................
I had to chuckle a little about your comment about not competing. I tell you what, my test mule is apart on my bench right now. I was shooting max power and getting really crappy air usage. Like .5 FPE/cuin. I think I found the problem... I hope.
But I can usually cut back to 80% power and use half as much air.
Good luck. (If you don't know the water vol of the tethered tank, I think we can calculate that.)
Lloyd
P.S. Bob, Please check my logic if you would be so kind. I appreciate having someone to catch my mistakes. ;)
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Bob gave me the water values of my tanks and I have recorded it . Might give me something to do this winter . I have a .308, .357 corsair , JH 32, 909- 32 that I can compair . Marvin
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Your logic on a regulated setup is correct.... My Hayabusa has a 22CI 3000 psi tank with the output regulated to 2000 psi feeding the tube on the gun which is 110 cc.... Since the reservoir on the gun never changes pressure, you only use the (water) volume of the tank before the regulator in the efficiency calculations....
Bob
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Bob,
Thanks.
Lloyd
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can you guys draw a piture or two to help us laymen understand?
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can you guys draw a piture or two to help us laymen understand?
Is there some particular part you are stuck on? The tethered tank setup with a regulator we were describing is kind of unusual and used mainly by the hardcore folks like Marvin who go through bullets by the truck load. Most folks will just be shooting the gun with no external tank hooked up.
Does that help any?
Lloyd
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I added a new fill calculator to this. Gene put a link at the top of the page in the GTA Library, or you can find it at calc.sikes.us (http://calc.sikes.us)
The new fill calc has a feature where if your big tank is only partially full, it can still calculate how many more fills you will get out of it. There is also a table listing cubic foot conversions for paintball tanks and air pack tanks that are rated in minutes.
I'm having fun doing the calculators, so if there is something else you might find handy, let me know. There is a little "envelope" icon on the calculator page you can use to email me if you want.
Lloyd
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Found this, searching for PCP effiency.. Really good calculator.
I had calculated it in ccm of air pr. Joule... being a "metric man" but wanting to find out whether my numbers where good or bad.
Printouts from the calculator.
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Not sure what you are asking.... and the printouts are hard to read (especially the 2nd one).... but it looks like the first one has very good efficiency, and the second one rather poor.... I'm guessing the second one has too hard a hammer strike for the pressure.... The HW100 is regulated, isn't it....
Bob
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Bent,
Yes, it looks like the gun is performing very well (air efficiency-wise) at 880 fps, but turning the power up to 958 fps, the efficiency takes a tumble. The calculator can be a handy analytical tool.
lloyd-ss
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Not sure what you are asking.... and the printouts are hard to read (especially the 2nd one).... but it looks like the first one has very good efficiency, and the second one rather poor.... I'm guessing the second one has too hard a hammer strike for the pressure.... The HW100 is regulated, isn't it....
Bob
50% showoff, and 50% asking if its correct.... 8) . Yeah, I can see the second one is hard to read... Just have the habit of resizing below 100kb from a danish forum. And its not my HW!
I recently got a brand new Cometa LYNX V10 MkII, and after tuning and breaking in the trigger I'm liking this gun more and more.. ;)
I had a spare 600mm HW100 barrel thats now fitted on the Cometa, originally it only had 470mm barrel.
The Cometa is regulated to 110 bar, with this rather low reg setting I assume its good getting 44 Joules and an effiency of 0,69. But turning the screw more gives very little velocitygain.
Low: 268m/s 150 shots @ 37 Joule
1 turn: 275
2 turns: 283
3 turns: 289
4 turns: 292 50 shots @ 44 Joule
8 turns: Max... 308m/s
Bent,
Yes, it looks like the gun is performing very well (air efficiency-wise) at 880 fps, but turning the power up to 958 fps, the efficiency takes a tumble. The calculator can be a handy analytical tool.
lloyd-ss
Yes Lloyd, as you stated. The lowest power gives the best effiency. ;D
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You are showing nearly a plateau in velocity as you increase the hammer preload past 3 turns, so I would back it off to there and call it a day.... I'm guessing the efficiency will jump up to about 1.0 FPE/CI or maybe even more at that setting....
Bob
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You are showing nearly a plateau in velocity as you increase the hammer preload past 3 turns, so I would back it off to there and call it a day.... I'm guessing the efficiency will jump up to about 1.0 FPE/CI or maybe even more at that setting....
Bob
I agree, I'll be testing the shotcount for 2 and 3 turns on the screw over the next couple of days.. ;)
And what i want is that the heavier pellets, 16grain and up should be around 270m/s. Thats the best speed for pręcision for most heavy pellets from what I have tested.
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That may be so, but you may not be able to achieve that without upping the regulator setpoint.... If you try and achieve too much with too much hammer spring proload combined with too low a pressure, your efficiency, and shot count, will suffer....
Bob
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Bob,
I am glad you have all these handy rules-of-thumb figured out. They are always helpful.
Lloyd
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IMO, the greatest tool for tuning a regulated PCP is to graph the velocity vs. hammer spring preload.... You will get a curve such as this....
(http://i378.photobucket.com/albums/oo221/rsterne/QB%20on%20HPA/QB78HPAVelocityandEfficiency.jpg) (http://s378.photobucket.com/user/rsterne/media/QB%20on%20HPA/QB78HPAVelocityandEfficiency.jpg.html)
Once you are on the velocity "plateau", adding hammer strike only wastes air.... I always tune my regulated guns to operated on the "knee" of the curve, which in that graph would be at 5 turns out.... Increasing the preload 2.5 turns (0.1") would only gain 20 fps and use over twice the air, getting less than half the number of shots....
Bob
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Been out in the wonderfull sunshine, with a buddy and two of my friends(HW110 and Cometa) 8)
Still need to fill out a few numbers but it seems like the optimal setting for the Cometa LYNX would be around 2½ turns of the screw... ;D
That also makes sense, as the same "engine" is sold as a .25
Thanks to rsterne and Lloyd.. ;)
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By that graph, anywhere from 2.5 to 4 turns should be OK, it's a matter of how badly you want power vs. shot count....
Bob
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By that graph, anywhere from 2.5 to 4 turns should be OK, it's a matter of how badly you want power vs. shot count....
Bob
Yes, the "Greed for Speed." I have it bad, but I know I am not alone.