*WIP* Energy transfer and joule creep.

This is a thing you need to take in to consideration when upgrading your rifle.
As this will matter if you’re going for a rifle with the best parts for the desired fps and bb weight.

Now i will go over 4 things in this guild, that being.
1. The energy transfer.
2. Joule creep.
3. Barrel ratio.
4. How the weight of piston affects this.
5. HPA and joule creep.

1. The energy transfer.

Okay first of ill go over the matter of energy transfer as this is the biggest contributor to both joule creep and the matter of cylinder to barrel ratio.

First of we need to understand the concept of energy transfer.
first of some RULES.

1. Energy cannot be created or destroyed.
Quote from Wikipedia ;link

“In physics, the law of conservation of energy states that the total energy of an isolated system remains constant—it is said to be conserved over time. Energy can neither be created nor destroyed; rather, it transforms from one form to another. For instance,chemical energy can be converted to kinetic energy in the explosion of a stick of dynamite.”

2.  Now this is technically not a scientific rule or law but it does apply as no one will have a 100% efficient system in airsoft (from the given fact that the most efficient system is still nowhere close to 90%)
the amount of useful energy is lowered by the amount of transfers needed. and the surroundings of the area the transfer happens (plus the materials the transfer is happening with) more transfers less power.
spring and piston. — 1 transfer–> air. –2 transfers–> bb. and this is even before you add in the friction of the piston and the friction of the bb down the barrel. (polish your barrels in other words.)
So the less transfers means less wasted energy. And well easier bolt pull, as the spring does not need to be so strong. case and point mancraft hpa system.

2. Joule creep.

Now on to the meat of the topic.
joule creep is in general the noticeable part of the efficiency of your rifle.
let’s say you shoot a .2 at 465fps or a .2 at 2 joule.
and you shoot a .4 at  400fps or a .4 at 2.9 joule.
With the same gun. Yes that is in fact possible if your gun is set up for .4g bbs and is not efficient at all with .2g bbs.

This is in most cases because the .2 bb is leaving the barrel before the piston and pressurized air has time to put all the “work” (scientific word for what the transfer is.) in to the bb.
And the .4 is well moving “slower” and it uses more time to speed up. but at the point where the .2 bb is at the end of the barrel it still has .9 joule it could have gotten if the barrel was the right length (or even more).
So the point is if the barrel is to short your best bet is the heavier bb. As it needs less speed to have the same amount of energy than the lighter bb.
.2g bb at 100ms = 1 joule
.4g bb at 100ms = 2 joule

3. Barrel ratio.

Now on the part of cylinder to barrel ratio you need more than 1=1 or a ratio of 1. As at this point the bb will start slowing down in your barrel before it leaves. Causing the air in front of the bb to have a higher pressure, and then trying to get past the bb causing it to start to bounce in the barrel.
Now the odds for this are indeed low but if you get close to the 1 to 1 (aka 1) ratio the chance is high and with a heavier bb it’s even higher.
Heck it might not even go past 1m, as it will most likely just roll out of the barrel.

Now you might wonder about how you find the ratio and well its pretty easy to find with this formula.
Or to make it simple R*R*H*π

So around the VSR-10 G-Spec.

R=11mm. H=80mm.
So the volum is ≈  30395,2mm3 (Note your answers might be different as I only used 3.14 as π)

And the barrel of the g-spec is.
R=3,05mm. H=303mm.
So the volume is ≈  8850,58mm3 (Note your answers might be different as I only used 3.14 as π)

Giving us a ratio of 3.4.

And on the normal vsr (given it also has a 6.1 ID barrel) we would get a volume of   ≈  12560,23mm3 (Note your answers might be different as I only used 3.14 as π)
Giving us a ratio of 2,4.

Now the bb weight to ratio is (this is partly tested) note it might be off by quite a bit if your piston is heavy.
Ratio <-> bb weight.
1.5 – 2 <-> .2g-.28g
2 – 2.5 <-> .28g-.3g
2.5 – 3 <->.3g-.4g
3 – 3+ <-> .4g- .5g Maybe even .6g if its high enough (and you can find .6g bbs. I have never tested this as I cant find the bbs).

Now to test the best setup, all you need to do is chrono it with the different weights. And see which weight gives you the most joule. (there is plenty of phone apps that calculate the joule if you have the fps/ms and bb weight) as the weight of the piston will also matter and change the joule creep.
Now for some tips when it comes to measuring your cylinder.

  1.  Disassemble the cylinder from the rest of the gun (all you need for this is the upper receiver, cylinder, piston and trigger)
  2.  Take the cylinder apart and remove the spring and spring guide.
  3.  Put the piston in the cylinder and put the cylinder back in the upper receiver.
  4.  Put the trigger back on the receiver and push the piston in til it locks on the trigger sear.
  5.  Hold the receiver and point it down (so the piston is in contact with the trigger sear and in the position it would be when the spring is there).
  6.  Measure the distance from the front of the cylinder to the front of the piston with a set of calipers (on my vsr cylinder this was 90mm on the dot).
  7.  Measure the length of the cylinder head and subtract it from the previous measurement (it was 10mm from the threads to the back of it, Giving me a total of 80mm).

4. How the weight of piston affects this.

Now another way of getting around the volume restrictions is to add more weight to the piston.
This will not remove any energy, (remember you can’t destroy energy.) but by doing this you will slow down the piston. And the initial speed of the bb.
And there by giving the system more time to transfer the energy.

now of course this can lower the final speed if you add to much weight. So doing this will require a bit of experimenting to see how much weight you need for the bb weight you want.
and for the technical people this is because of increased friction. and friction is a way the energy is escaping the system, as its then used to create heat.

All in all this can be giving you more joule creep and a higher fps. If its done right.
I don’t have a lot of things to point to, But i have seen this work. But in your case this is a thing you need to experiment with.

A great way of doing this is with hot glue and nails or other heavy ish objects that will not be in the way for the piston. (or heavy bbs as in .48 or there about)

5. HPA and joule creep.

There is a lot of talk around HPA and joule creep.
And as I see it, it’s the die-hard aeg users screaming that there is more joule creep in HPA.
And therefore dragging it down.

But the fact is that HPA has less creep than a spring powered system. And one of the reasons for this is point nr 4 (piston weight).
As the hpa system releases all the pressured air at once (in most cases) it creates less creep.
Some systems can release the pressure over a longer period of time, (p* is one of them) and this will then give some more creep but in general it will have less.
For instance my VSR-10 G-Spec has with a barrel ratio of 3.6 has 0.2 joule creep using the mancraft HPA system. (at 500 fps. tested with .2 .36 .4 and .43)
While a spring powered G-Spec with a ratio of 3.6 can have up to 2.5 joule creep or more depending on the spring and piston weight.

The main point is that in a spring powered system it is going to take longer  for the energy transfer. Than in the HPA system.
It takes around a second for the piston to reach the end of the cylinder. (In sniper rifles. AEG’s have a short cylinder compared to a sniper rifle)
While in a hpa system like the mancraft we are talking milliseconds.
After all a 0.2 bb traveling at 200 fps will use roughly 0.5 seconds leaving a 500mm long barrel.
And it takes around 0.01-0.05 seconds for the mancraft hpa system to start releasing the working pressure.
While a spring system will not have the working pressure before it has moved 1/4 – 1/2 down the cylinder.

(working pressure. is the pressure needed to get the bb moving out of the hop-up rubber and down the barrel.)
The short story is as follows.

The HPA system will give the bb the most amount of acceleration at the start, and after that the pressure behind the bb gets lower.
Thereby removing a lot of the joule creep.

While the spring powered system will in most cases still have a buildup of pressure even after the bb has left the hop-up rubber.
As the piston is now moving down the cylinder. And this is also one of the reasons the piston weight matters.
Thereby increasing the acceleration.

And there for the people saying that hpa has more creep than other rifles (aeg’s, gbb and spring) don’t know the science behind it.

References :

Reliku’s post on barrel ratios ;Link
1tonne’s post on joule creep ;Link

Final note.

This will be edited at a later date. And i will add pictures or maybe even a video to explain things a bit better.


2 thoughts on “*WIP* Energy transfer and joule creep.

  1. “It takes around a second for the piston to reach the end of the cylinder” thats wrong…. But else ok writing.


    • Well not from the tests i did. Then again i did it by sound so i guess i can redo the test with a camera, if I can get one with high enough frame rate.
      Mind you i guess I’ll edit it to specify that i meant for a Sniper rifle with a 400fps spring as the cylinder is longer.

      But i guess it’s off by quit a bit when it comes to AEG’s as there cylinders is shorter. (by a lot)


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