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Interesting test with 0.2g and 0.25g BBs
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01-04-2008 10:02pm#1In my usual style of self pimping, the below post is from my site airsofthacks.com: http://www.airsofthacks.com/2008/04/interesting/, just thought i'd post it here too, not a troubleshooting topic, but technical so likely of more interest to the people who frequent here.
Hands up if you’ve ever wondered about the difference in different weights of BBs? Accuracy, range, wind resistance? Well, here’s another factor which I never considered until recently. I read a post on arniesairsoft.co.uk in which the poster mentioned that using heavier bb’s could potentially increase the power output (i.e. Joules). Essentially what it boils down to is that heavier weight bb’s stay in the barrel longer, therefore get more time to accelerate than lighter ones.
To test this theory, I grabbed my favourite AEG (TM P90), which fires at a fairly consistent .95-.98J and some Excel brand 0.2g and 0.25g BBs, testing with the different weights gave the results below:P90/0.2g P90/0.25g 0.96 0.96 0.96 0.96 0.97 0.97 0.95 0.96 0.96 0.97
Theory smashed? Yea, that’s what I thought too, I decided to test it out with another device, conveniently I had my KSC G18c to hand which I loaded up with some gas and BBs, results are below:G18/0.2g G18/0.25g 0.85 0.95 0.85 0.93 0.87 0.91 0.88 0.94 0.89 0.93
Haha! That theory seems it might have some grounding in truth, well, to be a bit more sure, I tested with 2 more pistols which I had handy, a Meister Glock 17 GBB and a KSC Glock 19 GBB, yes I know, all Glocks, you either love them or you hate them and in my case it’s definitely the former, but don’t judge me on that, I own several other pistols which aren’t Glocks too
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The Meister Glock 17 achieved power outputs at:G17/0.2g G17/0.25g 0.66 0.72 0.64 0.73 0.66 0.71 0.65 0.69 0.64 0.72
And the KSC Glock 19:G19/0.2g G19/0.25g 0.78 0.87 0.8 0.89 0.8 0.87 0.81 0.85 0.77 0.83
So, what exactly is going on here? Well, the key difference is that the P90’s barrel is 247mm long, whereas the pistol barrels are only about 100mm long. The fact that the p90 has the same output power with both the .20’s and .25’s shows that the physical size of the BB is not playing a part in the extra power output, infact I measured a sample of both .20g and .25g BBs and found them all to be the same size (5.88-5.90mm).
The extra length of the P90 barrel in comparison to the pistol barrel gives the BB ample time to accelerate using the energy of the gas behind it (in this case, the air which is pushed by the AEG’s piston), however the pistol having such a short barrel causes much of the energy (in the form of gas) to be expelled out the end of the barrel after the BB has already exited the barrel. Using a heavier weight BB means that the BB spends longer in the barrel of the pistol and has more time to be accelerated by the expanding gas behind it, thus a greater amount of energy is transferred from the gas to the BB.
So not only do .25g BBs have greater resistance to wind, they actually make more efficient use of the energy expelled by the GBB, but in the case of the P90 with a barrel of 247mm, it made no difference. I’ll conduct some further tests on AEG’s with different barrel lengths, but I’m fairly sure that anything with a barrel of around 200mm or more will not see any difference in power output with different BB weights.
It is also important to remember that here in Ireland, the legal limit for any airsoft device’s output power is 1 Joule, using 0.25g BBs with a device which fires at 0.99J on 0.20g BBs may actually increase it’s power to above 1 Joule, care must be taken to ensure that you are compliant with the law at all times.
*Update:
I repaired my Cyma Glock 18 AEP last night and re-wired it with an external battery, so this morning I decided to conduct a few more tests, below are the results using .20g and .25g BBs as above.G18AEP/0.2g G18AEP/0.25g 0.32 0.31 0.33 0.29 0.33 0.3 0.32 0.3 0.32 0.31
As you can see, there is no noticeable increase as with the GBBs, infact with the .25g BBs in the AEP, the power output decreases. Theory busted? Well, no, not really, the Glock AEP has a much smaller gearbox than an AEG and a very small piston/cylinder to compress air in, so in this case, the volume of air in the cylinder matches the volume of air required to propel a .20g BB efficiently down the relatively small 100mm barrel. Were this a full sized AEG gearbox with a 100mm barrel, then quite likely the expected results of the energy level increasing would be seen.
I’ll be conducting a few more tests with this theory to try and get the most conclusive results possible, so check back for more updates soon.4
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[--SC(+)PE--] wrote: »0.25's for the win
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Your wrong.
0.23's for the win
- They are the perfect weight for our power limits. 0 -
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It was 25euro for shipping, which isn't too unreasonable when you consider the weight of BBs, but I get the impression they have a a fairly flat rate shipping charge for most international orders. No idea what the turn around time is yet, will let you know when I get them.
I haven't worked out the theoretical output of the tests yet and to be honest it would be quite difficult to do, as you said, there are way too many variables at play to accurately calculate it, plus it's easier to just do the test and see what happens
Thanks for the offer of the AEGs, I'll probably test with PSG-1/G36/M4/MP5/P90 to get conclusive results on AEGs, but I expect there to be no variance with any of the above since the shortest barrel of them all is over 200mm, I might pick up an mp5k at the end of the month though, it would bridge the gap nicely between the GBB pistols i'm using and the full size AEGs0 -
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true, shot to shot it does vary, but even though I only published the power results from 5 shots, I recorded readings for about 10, disregarding the highest and lowest values from the string and taking the median 5 shots.Alvin T. Grey wrote: »Can I throw a potential spanner int he works Keith?
Using GBBs probably isn't the best idea. Each shot dosn't get exactly the same volume of gas, it's inconsistant enough to throw out the test if you are going to such low tollerances.
You know, the seals cool down, the preassure in the mag drops. Reduces the explosive power of the gas.
These are just my thoughts on the matter.
As regards cool down, shots were taken approx 10 seconds apart, which should be plenty of time to prevent rapid cool down of the mag.
The results are also repeatable across different pistols, so I'm reasonably satisfied it's not an anomaly.
Having said that, I do agree with you, GBBs might not be the best test, so I'll hopefully be getting a mp5k to test it since it has a short barrel and also should have a fairly consistent power output from the gearbox.Alvin T. Grey wrote: »Maybe you could try again with the P90 and get a spread of results across two or three tests, rather than testing two or three different technologies.
The problem with testing using the p90 is that a short barrel is required for the different weights to have any effect, the relatively long p90 barrel allows ample time for any weight BB to achieve maximum velocity as it leaves the barrel.Alvin T. Grey wrote: »
Anyway, on an interesting side note. I found a problem with some of the chronographs.
It surfaced when I chronied my G36 twice. Once with the silencer, once without.
The energy recorded went up with the silencer attached. I think I have it figured out.
Just as you concluded the bb is still accelarating as it leaves the barrel. It meets resistance, wind, loss of air cussion whatever, and begins to slow. With the silencer attached it spends more time in an enclosed, still space and the loss of acceleration effect is lessened.
Many chronies don't allow you to shoot through them and require you to affix them to the end of the barrel. And as the measure velocity and don't take into account acceleration this means that what is under the joule inside the chronograph chamber may be over 10cm the other side......
I'm sure you'd nee rather percise equipment to measure that, but it is my theory anyhoo
That's interesting alright, I found that the silencer actually reduced power output.... I'll have to do more tests on that too 0 -
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