Airsoft Hacks

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:

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:

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 :).

The Meister Glock 17 achieved power outputs at:

And the KSC Glock 19:

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.

Thoughts/Comments/Suggestions? Feel free to click the comment button below.

*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.

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.

This entry was posted on Tuesday, April 1st, 2008 at 8:10 pmand is filed under Hacks. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.