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A quick reminder that the forums will be going down for part of today in order to be migrated. Don't be too worried.

Thank Christ it's back... I was having withdrawals there for a minute

I bought another stupidly expensive bit of plastic. Hopefully this stops my wrist from hurting so much

Ever since I started playing airsoft, and got involved in the whole game and science behind the guns and all this and that, to a deep enough level to understand it all, I have noticed joule creep. But it's only as of late that I've started to see it earn a name, and a gathering of people who actually seem to understand what it is. I first noticed it when I had an ICS L85 AEG, it was fitted with a 6.01mm tightbore barrel, 509mm long and fired .20s at about 360fps. I noticed that when I loaded heavier ammo, my fps wouldn't drop by as much as the conversion charts said it would. If you look at the equation used to work out muzzle energy, which involves the figures pertaining to ammo weight and speed, you'll notice that there's no mention of the length of the barrel, the bore width, or even the amount of pressure applied to the shot. Because it's just an equation, it isn't designed to be used in relation to airsoft guns, but it can be applied to them. As a result there are myriad variables it doesn't take into account, and this means that the conversion charts can be wildly inaccurate. The conversion charts are simply that. They convert the muzzle energy into different weight and fps amounts. It's like an on paper reference to using scales. Adding more of one thing here will balance out this thing here. The reality of it isn't so clear cut. Back when I first noticed it, the conversion charts said that loading .25s ought to reduce my fps by around 40, but I was seeing it drop by about 20. At the time I didn't realise that this would mean my muzzle energy was increasing, but it effectively meant that I was firing hot by around 20fps once I'd loaded the .25s. I was just counting my lucky stars that I was able to get away with having higher fps than the charts said I ought to be. However, now I've owned gas guns for a year, and I've seen it happen a lot more extremely, I've come to realise that the ignorance of not understanding it could lead to someone getting hurt someday, so my aim with this is to try and help bring attention to joule creep, and bring attention to... not how to counter it, but how to play with it safely. First, I'll try to better explain what it is and give an example of it. Joule creep is the name given to muzzle energy which increases when the gun is loaded with a heavier weight of ammo. The name, joule "creep" is given because the energy, measured in joules "creeps" up without it necessarily looking as though the muzzle energy has increased. It is common knowledge that adding heavier ammo reduces your fps, and many make the assumption that this drop in fps is a counter balancing effect which results in the muzzle energy remaining the same. You load .2s and chrono at 350, you load that same gun with .25s, you chrono at 315, muzzle energy remains the same. Right? Well, yes, sometimes. Joule creep is caused by guns sending more pressure down the barrel than the barrel can contain. Let's set up a hypothetical scenario: Gun A has a barrel which is long enough to contain 100% of the pressure that the mechanism sends down it in order to power the shot. So its cubic, volumetric capacity is large enough for all the pressure being sent down it to fit inside it. If you fire a .2g BB through gun A, all the pressure will be used on the .2, the .2 will leave the barrel and there'll be no excess air leaving the barrel once the BB's free of it. Adding heavier BBs to Gun A will see the conversion charts ringing true. Gun B has a barrel which can't contain all the pressure sent down it to fire the shot. It's only big enough to contain about 50% of what gets sent through it to fire the shot. So when loaded with a .2 it'll chrono at 350fps, but when the .2 is free of the barrel, it'll be followed out of the muzzle by 50% of wasted air. This is a gun that will see a lot of joule creep, because now when you add a heavier shot, due to it taking longer to accelerate out of the barrel, it is present in the barrel for longer, which means some of that "spare" 50% can be applied to the shot, and because more pressure is building up behind the shot, it is actually increasing the power of it. A .25 might use 60% of the air, a .30 75% a .46 95%... These are all just made up numbers to demonstrate the point, but can you see how a gun could gain power, that's muzzle energy, measured in joules. Kinetic, impact energy, that physically increases through the use of heavier ammo, all because the gun sends more power than required down the barrel. Joule creep is therefore significantly more prevalent in gas guns than AEGs. This is because AEGs use pistons and cylinders. Cylinders can only contain x amount of air, and they can be ported to reduce the amount of air they send down the barrel. Generally a factory AEG will be fitted with a barrel and cylinder combo that more or less match the barrel and cylinder's volumetric capacity, which will prevent joule creep from happening. Gas guns on the other hand, send significantly more gas down the barrel than required, simply by nature of the mechanism. It isn't something that can be reduced without it impacting the other performance characteristics of the gun. The longer and tighter a barrel is in gas gun, the worse the effects of joule creep will be. A longer barrel means there's more enclosed space for the gas to expand in, and the tighter the barrel means there's less space around the BB for the gas to escape. So I said I'd give some real world examples. A few months ago I set up my gas L85 to chrono at just under 370fps on .20s, because that's my regular site's limit. My L85 at the time was fitted with a 509mm long, by 6.01 wide tight bore barrel. Once set I changed to .28s which are what I generally run through it, and decided to chrono it again, just to gauge how much the fps dropped by. To my amazement, it didn't drop. I got more or less the same reading. In the ballpark of 370fps on .28s... I thought I might've got my ammo or my mags confused, so I double checked, but nope... According to conversion charts, a gun that chronos at 370fps on a .2 ought to drop to 312fps when loaded with .28s... But as I touched on above, this is because the equation assumes the same amount of pressure is being used to fire every weight of shot, but in gas guns, the heavier the shot, the more power gets applied to it. So My L85 therefore sends so much more pressure than it needs to down the barrel, that my fps remained the same because all the excess was making up for the drop caused by the weight increase. So if I'd gone to field this, I would have been firing hot by around 60fps, which is a joule increase of about .40. Today I thought I'd run the same test through my gas SCAR, so I chrono'd it on .20s, an average of 5 shots gave me a mean of 331fps. Loaded it up with .3s and did the same again, mean average of 290fps. According to conversion charts, 331fps on .20s ought to drop to 279fps, so that shows an increase in power of about 11fps from adding heavier ammo. Pretty significantly heavier too. My SCAR barrel is tiny too, I think it's 10" and it's not even a tight bore. That's a joule increase of only .08 or so, so it's pretty damn insignificant, but it proves the point that longer and tighter barrels, as per my L85 can take much greater advantage of it. Imagine if someone had a gas sniper, they set it up to fire at 500fps on .2s, it was fitted with a very long, tight as tight can be tightbore, and then they switched to .46s to play with... Ouch. So to be safe with your gas guns, ensure you look up the conversion charts, find the site's fps limits before you go, and work out what the limit will be on the weight you intend to use. Then when it comes to chrono, use the weight you intend to use, and set your fps to the limit you worked out. Conversion charts might not work with regard to the fps drop from adding weight being correct, but they are still correct in that x fps = x joules. So as long as you're setting your fps using the ammo weight you intend to use, you'll be safely within the limits. If you've read and understood everything I've just written out, or if you already knew about it, then help me spread the word. There are sites that ban the use of gas rifles because they don't understand the science behind the muzzle energy, or simply can't be bothered to deal with the need for people to chrono on the weight they say they're chrono-ing on. There are sites that force people to chrono using .2g BBs. This is ignorance, and it's potentially unsafe. Given any opportunity joule creep needs explaining in a way that people can understand and pass on, because the more people know, the less silly rules and regulations they'll be stopping us from using the guns that we love, for the hobby we enjoy.