Joule Creep

[AshOnSnow]

I’ve been reading about this thing called Joule Creep - I’ve heard it thrown around at game space before but never really understood exactly what it is and how it works. As I’m drawing ever closer to my DMR build, it seems this is something that is likely to play a fairly large role in the system that I choose. Could someone enlighten me?

[warlord]

[Iceni]

Joule creep is caused by a factor in fluid dynamics.

The force needed to move a BB is the primary cause of the problem. It doesn't affect AEG's in the same way it affects GBB rifles.

To move a BB requires a certain amount of force, To impart that force we use a volume of compressed air.

In an AEG the volume of compressed air we use is a constant, because it is mechanically defined. Adding mass to the BB does not increase the volume of compressed gas been supplied. The only way to add more energy is to compress the gas faster, Compress more gas, or reduce losses to compression. In the larger picture it is far harder to do this to an AEG on the field.

In a GBB rifle the volume of compressed air is controlled by a valve, a moving block, and the resistance of the BB (weight and friction). This is where the problems start. To make a low weight BB move at 350fps your gas needs to move both the BB and the Block, The block will have a fixed resistance based on the return spring, friction and mass (all constants). The BB however can be variable. A heavier BB in a well set hop will need more gas to move it, This volume increase also increases the energy the BB receives.

It is the same reason you get less shots per mag on heavier ammo with GBB rifles.



 

[Hangtight]

A system will tend to be more efficient in one configuration than another. In this case it is quite possible to build a gun that is very efficient with heavier BBs, and less so with lighter BBs. The outcome is that if you tune the gun to just get inside the chrono with light (0.2g) BBs, when you switch to heavier BBs, more energy gets transferred. So you chrono at a nice safe 1.45J (395fps with 0.2g), but when you're using 0.36g in your DMR it actually spits out BBs at say 1.65J, equivalent to 420fps with 0.2g.

HPA and gas guns can be tuned to exploit this more than AEGs due to the gas volume and pressures available. If you volume an AEG correctly for heavier BBs, it's naturally less efficient with lighter ammunition.

If you tune to most efficient at the weight BB you'll be using, and check that you're under joule limits with 0.2g and the heavies you've covered yourself. More sites seem to be moving to testing with the weight BBs you'll be playing with to try and make sure joule creep isn't being used to cheat the chrono.

[Jedi_Master]

 

A quick search on term "creep" may help as well:

 

 

[proffrink]

Basically a heavier BB fired from a gun leaves the barrel with more energy than a lighter BB fired from the same gun. As such, you should cronograph with the heaviest BB you intend to use that day and not the .20s they throw in your gun from their maraca mag at the crono table. Almost all sites will use a lighter BB than what you actually go and shoot, and this is where the creep gets in.

 

The problem itself stems from sites not knowing how - as @Iceni says - fluid dynamics works with relation to a force being exterted on an object when its surface area (i.e. the outside of the BB) is the same, but its mass/volume ratio is different (i.e. heavier BB but still the same size). The problem is exacerbated by HPA and GBBRs, where there's usually a lot of air being shoved down a barrel that can frequently be 'volumised' beyond what an AEG is. This can lead to people thinking HPA players are intentionally shooting hot when in reality they're using their .30s and .32s and are hitting you with more energy that usual. Again, a lot of the time HPA users are using heavier BBs than AEG users, and this too exacerbates the problem.

 

In addition, heavier BBs lose their energy less readily than lighter ones during travel for the same reason. That means they hit harder longer away, and is why you should always use the heaviest BBs that a) your hop can lift consistently and b) you're happy to throw money down on. They will go further.

 

Another way to solve this would be to ask for the weight you're using, then measure the fps (with that weight) and obtain the muzzle energy in Joules. Sites should really be cronographing in Joules instead of ft/s, but that confuses a lot of people who just want to throw plastic at each other, and that's fine. What I don't find excusable is bad operators letting non-malicious players take the flak for their lack of knowledge and ability to control the game. I've even been to sites where they ask 'what weight are you using' and have the applicable ft/s in their head to aim for - this also works, but is  less elegant solution than just taking the weight and speed and spitting out your muzzle energy. After all, the new restrictions are based on the muzzle energy of your gun in Joules, and not ft/s/fps.

 

Below is a chart that allows you to calculate Joules. Remember the limit in the UK for automatic stuff is actually 1.3J now. Anything over is considered a fully-fledged firearm. Here the chart says 1J is the limit.

 

[AshOnSnow]

So is it something one should use to their advantage, or avoid? And how does tuning the gas volume play a part alongside choosing which type of gas to use?

[proffrink]

It's something you should take note of, and something sites should know about because many are letting players shoot hot guns. Again, when they take your gun to the crono and say 'the limit is 335fps on a .20g BB' what they really mean is 'the limit is 1.04J' or:

• 300fps with a .25g BB
• 280fps with a .30g BB

etc.

 

However, sites have - for a long time - just been saying 'it's 335 with a .20g BB'. It's difficult to change the terminology that their players and staff are used to. The issue arises when site owners don't realise that Joule creep actually happens. They take a sniper rifle usually firing .45g BBs, or an HPA rifle firing .32g BBs, throw .20g BBs into it and then crono it - it's fine on the cronograph, but as the player at home has also been cronographing with .20g BBs too, Joule creep kicks in and as soon as they load that heavier weight they're shooting at 1.1J or maybe even 1.2J without noticing. Whilst a site could - in theory - explain their limits in terms of a list (like the above), it's easier to just give a Joule limit and let the player then look up what ft/s that BB needs to be leaving the barrel at.

 

To prevent this:

• Sites should just stop saying 'feet per second' and should outline their limits in Joules - this will confuse people for a while, but printing off some conversion charts like the one I posted above helps people visualise it quickly
• Sites should cronograph with the heaviest weight that player is going to use
• Players should cronograph at home using the heaviest weight they intend to use, or they might turn up and have their gun labelled hot at the crono

 

In terms of exploiting this is a player: The only thing you can exploit on this subject is that heavier will BBs travel further for longer (and this is not new info) and hit harder when they get there. If you can stomach the cost and your gun can lift it, switch to .30s or .32s - they will always perform better if your hop and magazine spring is up to the task. If you're playing CQB, this likely won't matter - just use .25s. If you try and misrepresent your gun by knowingly cronographing at home on .20g BBs, then switching to a heavier weight after you come away from the crono then you are consciously cheating and should be thrown out, frankly. The problem is that we're so deep into the 'fps' territory that most people don't realise they're going it.

 

I believe for HPA it's more pronounced because of the way the gas is delivered, rather than the amount (although HPA guns do actually put less air down the barrel due to this). Electric solenoid guns are tuned to release the air in a sharp gradient. AEGs deliver it almost linearly as the piston pushes that air out. In my experience the biggest difference comes usually not from the gun, but the fact that HPA players more typically spend the money on heavier weight BBs and thus Joule creep is more obvious. I couldn't tell you how the barrel air volumisation actually directly affects the BB - I've not modelled it and wouldn't have the knowledge to understand it even if I did. Again though, I think this falls second to the actual issue of BB weights.

 

So again, if you're using Joule creep to stick to the explicit site rule of something like 350fps with a .20g BB but are then walking away and putting .30g BBs in your gun, then I think that's unethical and really against the spirit of what the site limit means. I also cronograph at home with the heaviest BB that I use in that gun. It's not like I'm going to switch to a lighter one for half of the day anyway.

[Sitting Duck]

At a risk of getting my ar$e chewed........

 

@proffrink....

 

doesn't it roughly all work out the same chrono on 0.20's and use heavier weight as preferred ????

(on AEG's I mainly mean....)

eg:

 

350fps on 0.20's = 1.14j

now switch to 0.25's maybe slightly increase hop....

310fps 0n 0.25's = 1.12j

 

now it might be 315fps on 0.25's

think it is about 310 to 315 fps wise going from 0.20 to 0.25

which is about the same in joules

 

just saying the way the Mall does it is about the best method imho checking all stuff is on 0.20 for 340fps max

 

think it isn't quite cheating, perhaps slight bending of rules at worst but imho not cheating on aeg's

the next step is do we chrono with hop fully off or with it set

 

Think for gas or hpa there is the issue of joule creep

but on aeg's usually creep is more when we go from a short to long barrel and see a legit gun turn hot

(or vice versa if we drop in a much shorter barrel)

this long/short barrel assumes volume is sufficient for the barrel change

but often seen people put in a 300mm barrel in FireHawk or MP5k & go from 325fps to 385fps or something hot

[proffrink]

Well that chart isn't assuming your crono'ing and .20g and then switching weights. It doesn't factor in Joule creep at all if that's where you're reading it from. I just took the closest values for my approximations.

 

AEGs will creep just like GBBRs or HPA, but I believe most of the difference is indeed just in the weights people use. Perhaps the flat and R-hop buckings that're basically found in every HPA gun now are to do with it too? Conventional hops do slow the BB the more they're turned on because of that mound. Flat hops and R-hops apply that friction over a longer period and more of it goes into backspin than actually stopping the BB so that could be it too. I would say ultimately creep has become obvious in the past 5 years because a lot more people are putting up the extra scratch for heavier BBs - it's less to do with the power.

 

Sites should crono on your heaviest weight - it's the only way to rule it out. The Mall likely doesn't see creep as much as woodland as people - I would assume - aren't using .30g or sniper weights like they do at other places?

 

If you have some heavy BBs then testing this as home is easy enough so could be worth trying to help you visualise it. I think a lot of people are struggling with the concept, and that's fair enough given the walls of text (of which I've posted a couple) in this topic, but in principle it's far more simple. The solution is where people get confused.

[Adolf Hamster]

dont some chrono's have a joule calculation on them? i know mine does.

 

it's an interesting concept, first time i heard of it was when debating wether i should run .14's in my pistol as pellet travel time was a bigger factor in getting a hit than range or wind, of course in that scenario joule creep would work against you.

[proffrink]

Yes, but that still requires them to know what weight the BB is before it's shot. Then it's just a simple bit of arrhythmic to calculate the energy, which one can do with: KE ( in Joules) = 0.5 ( a half) x the mass of the something (in kg) x the speed squared (in Meters/Second).

 

http://www.airsoftmaster.com/fps-chart-for-airsoft-guns/

 

Oo they updated the chart:

 

[Sitting Duck]

Think the main issue is when people start messing with stuff imho....

on an aeg your basic energy is set minus the odd deviations between shot to shot

 

So in most aeg's your stroke/volume can't be easily changed - except for say ICS/Katana stuff

where you can quickly change out cylinder/port & spring etc.....

OK there is quick change spring malarky too

Plus there is the concept of taking say 400mm barrel gun, with a 120mm barrel inside

chrono on short barrel - then swap out barrel to 400mm and see fps/joules shoot up

 

ALL CHEATING $HIT like trying to make out 0.30's in mag are 0.20's at chrono

THIS IS ALL CLEAR OUTRIGHT CHEATING THE CHRONO - END OF

 

but most of the above requires tampering with the previously chrono'd setup

basically if anybody partially strips a gun in safe-zone that gun should be rechron'd - end of

 

So unless you mess with an aeg the joules/fps/energy won't really change

 

However on HPA the inlet pressure, the regulator & burst in m/secs can be adjusted fairly easily

so to increase the pressure & volume without a strip down in most cases

So it easy perhaps for somebody to switch to much heavier bb's AND compensate the power/energy to match

THAT - is blatant cheating like the aeg stuff I mentioned

and because it is easier to do few would notice the "adjustment" taking place by cheater

 

IMHO - switching weights on an AEG is not really cheating, as the energy kind of remains the same

adjusting the setup after the chrono though to compensate IS cheating

think some might think "Oh it needs a bit more oomph - let's tweak this...."

some might be unaware but think most people would know where their integrity is being adjusted also

 

Think for aeg stuff it all works out about the same

but if somebody partially strips/cleans a gun in safe zone, then they should themselves ask to chrono it once more

(if only all people were this honest without being asked to rechrono)

I would expect/suspect somebody "could" be perhaps altering stuff if I saw them strip a gun down

cleaning a barrel might alter fps a smidge unless it is really gunked up,

but a strip/partial strip - imho that gun should rechrono'd to ensure the energy still remains within limits

 

just my 2 or 3 cents

[proffrink]

Well, I still disagree slightly. The problem is sites not cronographing with the heaviest weights people are going to use. This is on marshals and site owners to check that they're being safe. In reality they're all just accepting a norm that's not been questioned in a long time.

 

However, if you know that you're susceptible to Joule creep and still crono at home on a light weight knowing full well that you'll pass with that .20g BB mag they use on site to check your gun (but are going to use .30g when you put your own mag in) then yeh, you're cheating. You're not going to get caught because the marshal knows even less than you do, but you're a piece of shit, shouldn't be playing and - if you're using HPA - are just adding to the pile of excuses to get it unrightfully banned from your local when people keep complaining that they suspect you're firing a hot gun.

 

If you don't know and sites haven't explained it then frankly I'd accept ignorance as an excuse in this case as it can be confusing for many people. As such I wouldn't call it 'cheating' given the lack of intention. I feel there's probably only a very, very small subsection of people who're consciously exploiting Joule creep for nefarious reasons. Most just have no idea it's going on with their gun.

[Rogerborg]

Practically speaking we're reliant on players being honest and aware, but that applies to most of this game.

 

Education seems to be what's called for, although there's probably an argument to be made in favour of sites testing with something like (site provided) 0.3g rather than 0.2g.  Heck, bulk bought 0.4g would only add pennies to the cost of chronoing.

 

Are there any argument against doing that?

[proffrink]

That's exactly what I'd propose, yep. Or just the odd spot-check on people's BBs (every 10th person just get them to pop a couple of BBs out to be weighed. Everyone else can just say.

 

Think we discussed this in a very similar thread last year.

[Adolf Hamster]

i've heard of sites that aren't too fond of hpa because it's so easy to adjust firing pressure, i know for my new aeg design the reason i went with a spring as the main energy source was to stop people being able to adjust fps electronically for that very reason.

[proffrink]

It's not if you have a tournament lock, which are a couple of quid. If a site is worried then it can require them.

 

Thing is a lot of people do complain about HPA players for having easily adjusted their regulator when it could very well just be unchecked creep. Taking an allen key out in the safe zone and fiddling with your regulator pressure is about as hard as changing a quick change spring on an AEG anyway.

[Adolf Hamster]

2 hours ago, proffrink said:

It's not if you have a tournament lock, which are a couple of quid. If a site is worried then it can require them.

 

Thing is a lot of people do complain about HPA players for having easily adjusted their regulator when it could very well just be unchecked creep. Taking an allen key out in the safe zone and fiddling with your regulator pressure is about as hard as changing a quick change spring on an AEG anyway.

 

true, my local tends to use zip ties, although the guys there that are running hpa are good honest players so it's not so much of a problem.

[Immortal]

Interesting topic and info. Thank you for the read 👍

[Chris_B]

I made my own graph on the joule creep. I know there's loads already done out there, but it's a way of learning it by creating your own I guess.

 

I only used 4 variants of BB weights for my graph, but you can visually see the gaps between each weight, which is the variation in energy applied to achieve the same velocity to the BB weight below it.

 

To understand it better, you chrono your gas gun on 0.20g to get 350fps (for instance, I know it's not a target), great! Your gun is legal on 0.20g as you get 1.1381J, but then you switch to your preferred playing weight of BB. You then chrono it again, and your velocity is higher than what the table says for your weight, to which is shown in the BB weight column in the attached table.

 

So in reality, you should chrono on your playing weight, refer to the chart and then adjust your gas valve or whatever to achieve that velocity which will tie up with the energy value, this takes the error out, as the gas expands when using green gas, propane, HPA, etc. as opposed to mechanically compressed inert gas (air).

 

I'm still learning about gas guns, so please, any information I have divulged incorrectly, please put me right (in a nice way 😁)