A Question About FPS Limits

[leewardgrand]

Hi there.

If I am doing an event that states an FPS limit of 400FPS with a .20g BB does this mean that I am allowed to use a .25g BB in the event as long as I chrono under 400FPS with a .20g? I understand that if I chrono less than 400FPS with the .20g then the .25g should also be under.

Or am I to chrono under 400FPS with the .20g and strictly use the .20g in the event.

Thanks for any help.

[Styrak]

Usually it means you chrono with 0.20g, then you can use any weight BB you want.

Some places like CQB facilities say "0.20 only" but that's usually rare. Always follow the field/facility rules.

[Drake]

Like Styrak said, the "400 fps w/ .2g" is a standard measure, its not just 400 fps with any BB weight (in which case chronying 400 fps using .30g BB, for example, would yield a much higher velocity when using .20g).

Usually events let you use whatever BB weight you want, although there are some exceptions, usually in indoor/CQB games where engagement distances are reduced (heavier BBs have more inertia and carry energy further, so at short ranges the energy in impact is closer to point blank shot, increasing the risk of injury).

Note that some organizers opt to use muzzle energy as a limit instead, so they'll chrony guns with whatever weight BB you're using on the field and calculate muzzle energy (or more precisely, they have a pre-calculated limit chart for all BB weights) -- the limit usually being ~1.5 joules which is roughly the energy of a 0.2g projectile at 400 fps.

[FirestormX]

The unstated idea is that you chrono with .2s, and then game with whatever weight you want.

As Styrak said, certain places will not allow you to use heavier weights. The reason for this, is that even though you have a slower muzzle velocity, the heavier mass of the BB allows it to hold onto that energy for longer.

In a very exaggerated example with made up numbers, say you owned a CQB facility where lightbulbs are exposed, 20 feet off the ground. If someone accidentally shot a .2 straight up at 400 FPS (~1.5 joules), it might lose a lot of its energy on the way up, and only impact at 300 FPS (0.8 joules of energy). If you shot a .3 straight up at 325 FPS (~1.5 joules), the mass would cause the BB to lose less of its energy to wind resistance, and might impact the light bulb at 300 FPS, conveying 1.25 joules, which may shatter the light bulb.

So the reason for chronoing at .2 is because that's the arbitrary industry standard that is used when calculating joules (you could chrono at any weight, since it's just one variable in a formula). But the reason you may not be allowed to go higher, is because the mass of the BB would allow it to retain the energy further out from your muzzle.

In most cases, that's not an issue, especially outdoors, so generally you can assume that you can use any weight for actually playing, unless otherwise stated.

Edit: ninja'd by Drake

[leewardgrand]

Thanks very much, everyone!
My question has been answered.

[lurkingknight]

a .2g bb @ 400 fps is 1.48J

Why most people use a .2 is because they're inexpensive, and as a game organizer, I can buy a big bag of them and chrono everyone to make sure their guns are shooting 1.48J.

Where this falls apart is just because a gun shoots 1.48J with .2s doesn't mean it will shoot 1.48J with heavier ammo. Phsyics happens and you can in reality shoot 1.48J with a .2 but 1.52J with a .32 or whatever... it can be higher due to the way the air charge is delivered. It's not so much on an AEG but on guns that use expanding gas, like gbbrs and polar stars, you can see a lot more J with heavier ammo.

It's important to remember that your gun should shoot under field limits with the ammo you're going to use. So YOU as a gun owner should be looking after this. If you don't know how, ask your gun tech to chrono your gun with the ammo you shoot and calculate the J by hand.

Why measuring with the ammo you're going to use isn't practical (on a game organization level)

Is that I show up with a bag that says .3s What's to say I didn't empty that bag and load it with .36s which will shoot harder in my setup?

Or I show up with a bag that says .25s that will chrono 350 but in fact they're .2s that chrono 430? It becomes hard to prove what you're shooting to the naysayers that will accuse you of one or the other, and if the chrono ammo is provided by the game staff, it becomes logistically difficult for them to provide a whole slew of ammo weights to do the chrono with.

So chronoing with .2s is the easiest way to get some sort of conformity and logistics simplicity by organizers to make sure everyone is at least close.

If it were me I'd have everyone chrono with .25s to make sure they were all 1.48J At least be in the middle of the weight variances to get a closer reading of what the gun is really outputting... since most people use .25s anyways.


A guy I tech for owns a polar star. He assumed that because his gun shooting 400 with a .2, but when he chronoed with his .32s he was shooting 350fps. A .32 with 1.48J of energy should be closer to 310fps. In this case, he didn't know any better when he started playing with his output settings, but this is a perfect example of people needing to chrono with the weight they will be shooting. His gun is technically not field legal, even though he shoots <400 with a .2.

[Drake]

Originally Posted by lurkingknight

Why measuring with the ammo you're going to use isn't practical (on a game organization level)

Is that I show up with a bag that says .3s What's to say I didn't empty that bag and load it with .36s which will shoot harder in my setup?

This is a whole other can of worms, but I find this to be a slippery slope. If someone's going to swap BB weights into a different bag, then they're going to swap their PTW cylinder after they chrony, they're going to open up their NPAS a quarter turn, they're gonna quick-swap their spring with a stiffer one, they outright just won't call hits, etc.

Cheater gonna cheat; that's why a zero tolerance stance must be taken.

[lurkingknight]

yes, but intent to cheat and simply not knowing that a heavier weight can shoot harder than expected are a bit different.

a .2 at 400fps as verbatim is quite misleading.

There are pros and cons to using the .2 standard vs using shooting weight standards which is what I was trying to allude to.

[Hectic]

i agree with lurking. Its like the sniper limits, i am expected to shoot safely when running 500fps, if i run .36's i can safely shoot with a 150ft med (not tue standard 200) due to energy loss over distance making a shot at 150ft having about the same energy as a 400fps aeg shooting .28's at about 50-75feet. Put some 43's in there and suddenly even the standard 200ft med is pushing it a little. Im all for joule chrony not fps, but at the same time like stated its a lil difficult to keep changing your chrony for different bb weights.ad hard to know for sure if the guy who says hes runnin 28's isnt running 32's ect.

[ThunderCactus]

Originally Posted by FirestormX

(you could chrono at any weight, since it's just one variable in a formula).

It's only one variable in a basic formula, but doesn't account for the fact heavier ammo could result in higher muzzle energy

Originally Posted by lurkingknight

If it were me I'd have everyone chrono with .25s to make sure they were all 1.48J At least be in the middle of the weight variances to get a closer reading of what the gun is really outputting... since most people use .25s anyways.

^THIS
Except I'd do it with .25 indoors and .28s outdoors for the same reasoning

Chronoing on .20s, then switching to .30s could account for a .3j (~50fps) variance, sometimes more.

No, you can't trust everyone to be truthful about the ammo they're using at chrono, but if you chrono them all with heavier weights, we at least know as fact that joule creep generally swings one way.
So although some guns do have more muzzle energy shooting .20s than shooting .30s, an argument can be made that even if they're 20fps over on the .20s it's irrelevant since the light ammo slows down much faster than heavy ammo.

So really, it makes the most sense to chrono with the most popular ammo for that particular game. Usually either .25s indoors or .28s outdoors.

[Ricochet]

I agree with Drake. There's too many variables on too many guns to stop people from cheating in this way. Chronographing exists for only a few reasons. For starters, all guns can be tagged. Which means you've physically seen every gun to come through. No one can claim that they chrono'd a gun that doesn't have a tag, after being caught cheating. Secondly is to check that each gun is capable of shooting appropriately. This will eliminate any guns that just run hot no matter what you do. There's a few more, but between gas expansion, hop-up adjustments, and switching ammo weights, there's just too many variables. I run a gun that I can switch out ammo weights without significantly increasing joules up or down. But certain gas systems cannot. An AEG shooting a 0.20g BB at 400 FPS may shoot a 0.25g BB at 360 FPS. With a gas gun you might get 400 FPS on a 0.20g but then get 395 FPS on a 0.25g. This is just for muzzle velocity, and not for BB weight or joules necessarily. The most effective method of chronographing would be joules over FPS, because that is relative to all things. However, not all gas platforms will behave the same way.

However you slice it, I believe that all players must chrono with the same weight and brand of BB. So essentially the game host must supply, but at least you have a solid base to start. Another thing I believe is to have a hard cap and a soft cap. The soft cap is your velocity and energy goal, and the hard cap is the concrete end of the line. So if 400 FPS, or 1.48j, is your goal with a 0.20g, then you have a 20 FPS safety window, bringing your hard cap to 420 FPS, or 1.64j. So this allows for temperature change, as well as those guns that can't find a happy medium. So if your AEG is tested with a 0.20g and shoots 402 FPS, you're fine. But if it shoots 421 FPS, your are not under any conditions allowed to field that gun. Also, the hard cap applies all day, and players are responsible for their guns behaviors. So if at 09:00 AM, it's 15•C out, and your GBBR chrono's 418 FPS on a 0.20g BB, and you expect it to hit 25•C by noon, it's no good. So if they can get it shooting 395 or 400 FPS, then you've given them a 20 FPS safety window.

As has been said above, zero tolerance. Yes a player can lie about weight, or swap springs, etc, but you could still figure it out by chronoing him after a complaint. If they are caught, ban them. After the first one or two guys get permanently axed, most of the others willing to break the rules won't.

I like Thunder's idea, but you cannot enforce BB weight past the chrono phase. Not to mention, players should be able to switch it up. There's only one surefire way to stop dangerous guns. By the way, safety and sportsmanship are the whole point of chronographing pre-game, not to catch cheaters. Cheaters are caught after the fact. If I was concerned about any gun during a pre chrono, I'd ask them to chrono with a 0.20g, a 0.25g, and a 0.30g, just to see the guns behaviour. Seriously though, chrono 0.20g and 0.32g, one right after the other. With a hard cap on FPS and joules, you can't go wrong. BB weight of any kind must fall within the appropriate limits. If buddies WE M4 Open Bolt shoots 399 FPS on a 0.20g and 391 with 0.32g, then guess what? He has to downgrade to play; period. If someone switches out parts or changes adjustment on the field, then you'd have to catch them during play regardless. Spot checks anyone? I like admins who keep their armbands in their pouches until they need them, and have chrono's only a radio away. Ask the player to put his gun down until a chrono arrives. He can't switch magazines or adjust anything. If he refuses, he's banned. It's pretty simple.

[ThunderCactus]

The idea behind chronoing with .28s is you get the best foresight of joule creep
It's not perfect, since if they're at the limit with .28s then there's a good chance they'll be over if using .36s, but it's significantly safer than chronoing with .20s and guaranteeing that they'll be over no matter what ammo they use.

I had discussed this with two other admins, there's ALWAYS a way to cheat the chrono, it's just a matter of lengths a person goes through to do it. Regardless, the penalty is the same for any severity of cheating the chrono.
The most surefire way we could come up with was:
-The host has custom, colored orders of BBs; one color for each .25, .28 and maybe .36
-The player buys ammo from the host, chrono's with said ammo, and receives a tag of the same color
IE .28s are yellow, chrono with yellow BBs, get yellow tag.
.36s are red, chrono with red BBs, get red tag.
-Punishment for people not using their color of ammo
-Severe punishment for outside ammo
-Easy to spot check, you know what weight they have, just need to chrono against the max fps for that specific weight. Super easy to catch people abusing the system.
-tamper-proof stickers for PTWs, AEG with quick swap springs, tourny locks for P*s, etc

Problems that arise even with this method:
-P*s have tourny locks to prevent adjustment of fps, however, their control boards are not locked and you could potentially adjust the fps by a LOT just by changing the volume of air used per shot. So like long barreled P*s (which most P* users have a 509mm+ barrel) can use low volume for chrono, then crank up the volume creating joule creep, without ever adjusting the regulator.
-GBBRs, NPAS can be adjusted and the obvious temperature creep issue
-Find me an admin that can spot an AEG with a quick swap spring feature. I've worked on dozens of them and I can't spot them without opening them.
-Someone could go way out of their way to get something like a .36 custom made in yellow, fooling the system.
-Someone could tag their own guns

So really unless you're building and tuning EVERYONE's gun, or strictly using rentals, it's extremely difficult to fully control the fps of everyone on the field.
It's still very much an honor sport, and part of that is being honest with your gun's muzzle energy.

[Ricochet]

Let's say I agree with you, and I kind of do, then I'd recommend shooting with a 0.32g or something to ensure his joules are under control.

[lurkingknight]

That would be the best solution.

Your gun is always going to joule creep up... it will never go down.

For example, my g36 creeps. It does 380 with a .2 which is 1.42 or something like that.

It does 305-310, which is 1.46 or whatever.

You're always going to get the higher joule reading from the heavier ammo. It will never work the other way around, so your velocity with a .2 almost becomes irrelevant because it will be well under 400 in those kinds of setups.

In a graph you'd expect the J to be a constant flat line as you go through the weights of the BBs, with J creep you're going to get a / bias, so if the heaviest weight is still under 1.48J your lowest weight is going to be well below.

I doubt you'd ever see a \ bias graph where the left would be over 1.48J and the heavier weight would be well below. That would probably indicate some sort of major compression failure or bleeding of your air charge somewhere. At least, I have not observed one come through my hands, built by me or handed to me that way. So I can't say I've observed it happening.

Also it becomes harder to fool the chrono with joule creep and adjusting your hopup. More hop which slows lighter bbs down actually has the reverse effect on a well sealed joule creep setup... the pressure builds more, the acceleration is faster in the same amount of distance, you get more joules when you dial up the hop. I've tested this with my g36 on my chrono. It oddly builds more fps the higher I dial the hop and then eventually it will just compression jam and not shoot.

In reality I think it would probably make most sense to chrono a game organizer provided high and a low weight to be on the safe side.

at 1.5 J there's almost no need to be shooting heavier than .32 or .36 I've yet to try .36s but 300fps with a .32 is plenty slow enough for me. lol.

[ThunderCactus]

Joule creep CAN work in reverse:
Wherein you have a cylinder that's under-volumed to the barrel, a heavier BB would only have pressure behind it for less than the full length of the barrel, resulting in limited acceleration. Whereas a lighter BB would have time to reach the end of the barrel before the air lost pressure.
Or in a system wherein the hopup can't handle heavy weights, forcing the user to crank it up and subsequently losing serious fps on heavy rounds, but being able to run at a minimal loss on lighter rounds.
It's also conceivable in a system with an air leak, whereas a heavier BB results in higher pressure and therefore more leakage.

My point on that was even though joule creep may work in reverse in some cases, it's far less dangerous to be 5-20fps over the fps limit when using .25g or lighter due to the fact it decelerates faster.
So chronoing with heavier ammo controls the more dangerous and common end of the spectrum.