Chrono: FPS vs Joule for gas guns

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Chrono: FPS vs Joule for gas guns

Post by Rabid-Weasel » Mon Feb 17, 2014 10:06 pm

From our Friends at, and some known confusion you might see about FPS v. a joule rating for P* and other gas guns.
Hello everyone,

I know this topic has been covered but it keeps coming up and I want all the information to be here for people to find. Lots of players/field owners do not understand how the P* works... which leads to silly rules/assumptions.

So to clear all that up, here we go:

A Polarstar shooting 400fps with a .25g BB will be putting the same amount of energy/power (joules) into a BB as an aeg shooting 400 fps with a .25g BB. The original poster also wanted to know why fields are so concerned about having a different chronograph policy for P*s and other gas guns.

This question came up when a local field of theirs posted that they were having issues with P*s and that they will be changing their chrono procedure. The field owner stated that a P* shooting at 400fps with a .25 has a different energy output than an AEG also shooting at 400fps with a .25g.

The Answer:A PolarStar shooting 400 FPS with a .25g BB DO produce the same joule output as an AEG shooting at 400 FPS with a .25g. So the field owner was incorrect at saying this, but I understand the reasoning for why he is doing the rule change... this comes down to "Joule Creep", which is evident in all gas powered guns. It also can be done with AEGs by doing certain things we will not get into, but it is less evident and not as common. However, it can be done.

So... now onto the evidence that this happens and the appropriate measures for chronographing gas guns or for that matter ALL guns on the market. Most places chrono in FPS (Feet Per Second), whereas if they use Joules, they can get more accurate readings and make it harder to "cheat" a chrono or have to worry about energy creep... However in order to do this, when chronoing, a player must use the weight they intend to use. This is where it gets a little tricky.

One example of this, is that OP: Lion Claws is requiring P*s to be chronoed with a .32g BB at X Joule. Now the one thing to note here is that if a player chronos at the limit joule with a .32g and then uses .25g, they are actually going to be under the limit (Not that the limit should be the goal, I'm just using this as an example). If that same player uses a .40g, then that player will actually be over the limit. So in the end, the only way to be 100% is to use the BB that a player is using.

The only catch to this is that it leaves room for cheaters, who would say they will be using .25s and then later switching to .40s. The compromise to this is using a heavy weight BB such as a .32 or .40 to chrono. A field will probably pick a joule energy amount they are comfortable with, account for plus or minus joule amount and go with that number. This should give you an idea of what is going through a field owners heads when making the decisions that they are when it comes to chronographing.

So now the testing to give you a better idea of what you will see with a P* vs a typical AEG.

Test gun 1: Classic Army M15A4 Carbine
Test gun 2: VFC SR16E3
Test gun 3: CQBR P*

BBs used:
Airsoft Elite .20g
Bioval .25g
Echo1 .28g
Bioval .30g
Madbull .40g

Gun 1 (CA M15A4) at 382 FPS with .20g:
Airsoft Elite .20g - 382 FPS - 1.35J
Bioval .25g - 350 FPS - 1.42J
Echo1 .28g - 328 FPS - 1.39J
Bioval .30g - 307 FPS - 1.31J
Madbull .40g - 251 FPS - 1.16J

Gun 3 (P* CQB) at 382 FPS with .20g:
Airsoft Elite .20g - 382 FPS - 1.35J
Bioval .25g - 362 FPS - 1.51J
Echo1 .28g - 350 FPS - 1.58J
Bioval .30g - 340 FPS - 1.6J
Madbull .40g - 302 FPS - 1.69J

Gun 2 (VFC SR16E3) at 340 FPS with .20g:
Airsoft Elite .20g - 340 FPS - 1.07J
Bioval .25g - 310 FPS - 1.11J
Echo1 .28g - 289 FPS - 1.08J
Bioval .30g - 269 FPS - 1.00J
Madbull .40g - 226 FPS - .94J

Gun 3 (P* CQB) at 340 FPS with .20g:
Airsoft Elite .20g - 340 FPS - 1.07J
Bioval .25g - 316 FPS - 1.15J
Echo1 .28g - 303 FPS - 1.19J
Bioval .30g - 294 FPS - 1.2J
Madbull .40g - 258 FPS - 1.23J

As you can see, even if someone chronos both a P* and an AEG at the same FPS, Say 400 FPS, their joules will be the same. Once the P* player uses heavier weight BBs, the joules continue to climb whereas an AEG will climb slightly and then diminish below it's original value once too heavy of a BB is used. This leads into a whole other topic of what BB is too heavy for a P*? As you can see the joules keep rising. Just some food for thought.

So there you have it. Just wanted to share this with everyone in case more players didn't understand the concept behind this.

Thanks everyone!

Edit: A couple more thoughts that Mike Gin mentioned to me that are good points that I accidently left out. (Thanks Mike!)

1.) Instead of chronoing just P*s with heavier weight BBs, AEGs should also follow suite. The joule rating will be different depending what weight BB is being used... so the field owner would have to determine what joule is closest to the limit they want and figure out which weight is a good compromise to go with, unless they go with what the player uses (Obviously this is a big trust issue and would allow cheaters to come into play).

The main thing with this is you want to make sure you pick a BB weight that will work for joules in the FPS range that makes the most sense. IE: if the limit is 300 FPS (x Joule), you wouldn't want to chrono everything with .40s... If the limit is 500 FPS (y Joule), likewise, you wouldn't want to chrono with .20s.

2.)SPOT CHECKING! If you want to be safe at your field.... do spot checks. This keeps everyone honest and discourages players from cheating if they intend to. Also don't just spot check P*s, spot check everyone!

Now that gas guns are more prevalent here in the US with the P*'s popularity rising, it's going to be up to field owners to adapt and start going the way of the joule vs FPS. Yes FPS is safer... but joules are more universal and more true to the correct energies being utilized.
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~MAA Member #91

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