Enforced BB weight limit

[MalcyFett]

I’ve had a good few months away from Airsoft, on my return I’ve been advised that the usual sites my chums visit have BB weight limits now for outdoor sites.

Gunman, GZ and UCAP all saying max weight of .32g on HPA/AEG/GBB.

I generally use .32 anyway, but curious if this is now the norm for most sites.

 

[Hami]

First I’m hearing of it 

 

[Adolf Hamster]

It's a rule that has some logic behind it, ablbeit the lazy logic of a site that finds it easier to enforce an unenforceable rule than take the steps to ensure proper chrono practice.

Tl:dr is hpa/gbbr has a tendancy to joule creep, ie it can fire kosher joule-based owchie on 0.2g but significantly more than the allowable joule-based owchie on heavier rounds, so a (theoretically unsuspecting) player can pass chrono with flying colours and with no more effort than loading their preferred heavyweight ammo be dishing out unnessecary zingers to their fellow humans.

 

[Rogerborg]

It's not generally accepted yet, but I'm fine with it. Above about 0.4g you have to mix in so much metal and minerals that it becomes hard to argue that we're slinging "plastic".

 

[Galvatron]

UCAP doesn't surprise me and I think it's reasonable.

With a weight cap, it saves having to enforce an MED in the CQB areas of their mixed outdoor and indoor sites. At least that's what I assume the rationale is.

 

[GiantKiwi]

It's actually fairly common up here.

Which would be fine, except its not founded in logic or understanding of physics.

 

[Rogerborg]

Which would be fine, except its not founded in logic or understanding of physics.

Why don't we shoot each other with steel BBs?

 

[Anonymoose]

Why don't we shoot each other with steel BBs?

100% biodegradeable!

 

[Cannonfodder]

I've only ever seen it at cqb sites where shooting someone with a heavier bb is going to cause more pain.

UCAP doesn't surprise me and I think it's reasonable.

With a weight cap, it saves having to enforce an MED in the CQB areas of their mixed outdoor and indoor sites. At least that's what I assume the rationale is.

That makes sense. Restricting certain weight bbs to some areas of the site would be a ball ache for players to stick to and almost impossible to enforce by staff.

Of course if the site doesn't have cqb areas then its a bit pointless imo. If it's done to try and prevent joule creep then surely its better to just chrono on whatever weight is used in game

 

[Hatchet]

This thread needs more science.

Assuming rounds weighing 0.2g and 0.4g leave the gun with the same kinetic energy (joules), what's the difference in impact at point blank/10m/20m/30m? 

The heavier round can't *gain* any more energy (although it can lose it less quickly).

Brain hurts.  

 

[mightyjebus]

There are smarter people on here than me but as far as I remember from school:

Velocity and Mass are inversely proportional, so it takes a 0.4g bb twice as long as a 0.2g bb to get to it's maximum velocity. based on a 1J AEG then somewhere along the flight time the 02.2g BB will reach maximum velocity and at double that distance the 0.4g BB will do the same.

o.2g and 0.4g BB's will have different momentum on a static object (i.e. a person) and the Mass + velocity will be transferred as momentum to the solid object. If you increase the mass or velocity then the momentum transferred will be greater. 

Velocity and Mass are why you get Joules creep. If the BB hasn't fully accelerated by the time it goes through the chrono then you don't actually know the power the BB has. So more mass (0.4g BB) plus Joules creep = more momentum which translates as harder impact.

In CQB at close ranges the 0.4g BB will transfer the Mass, gained momentum and any velocity still to be used up as the BB was accelerating so you don't loose anything even if the BB hasn't got to full speed.

The momentum (impact) will vary on the static target depending on the angle that it was struck and the material is is made from (plate carrier good, exposed flesh bad).

 

[Hatchet]

But isn't joule creep the heavier bb continuing to receive acceleration force in the barrel after the point at which lighter BB would have already exited? (and this only when there is more acceleration i.e. cylinder capacity, left to give). At the point its *left* the barrel, it surely can't have any more acceleration force acting on it. It demonstrably can't be the case that if you chrono'd it 20m out it would have more energy than previously, right?

(Disclaimer, I don't know any of this stuff and have been drinking, so...)

 

[mightyjebus]

it depends on where the BB reaches maximum acceleration. If it's inside the barrel then the energy measured at the muzzle will be the maximum joules it can achieve. A heavier BB could still be accelerating as it leaves the muzzle and doesn't reach maximum velocity until xx distance (double that of a 0.2g BB). Another way to think of it is the BB has had the energy applied but it takes time (in our case distance) before the full effect takes place. Think of a rocket taking off, it doesn't go from zero to maximum right away, it slowly creeps forward and accelerates every meter it climbs until it's at full velocity. The rocket power is the same at 0 feet as it is at 1000 feet but the rocket is travelling at 2 different speeds at those 2 distances. (ignore the fact that the rocket is fighting gravity and we will be fine with this analogy).

I suspect that part of the reason for heavier BB's to travel further is that they are accelerating for longer so don't start to slow down as quickly as a lighter weight BB which reaches maximum acceleration quicker over a shorter distance, reducing the overall flight time compared to a heavier BB. Friction will affect the heavier BB more and gravity will also have some effect but it doesn't seem to be linear when comparing 0.2 and 0.4g BB's

One way to test this would be to line up a couple of chrono's and shoot some heavier weight BB's through them to see at what distance the BB peaks in joules.

 

[John_W]

Once the BB leaves the barrel it will start to decelerate. There may be some slight residual acceleration from gas/air exiting the barrel but that would be negligible and only for a very short distance.

Ye cannae break the laws of physics...

 

[mightyjebus]

Scottie will be spinning in his grave. The velocity and Mass will be applied inside or outside the barrel depending on where the BB reaches maximum acceleration. A cylinder/hop/barrel combo can only supply X amount of energy and it doesn't matter how long the inner barrel is after a point as it will add nothing extra as you can't have something for nothing.

There is a chance of a BB starting to deaccelerate inside an inner barrel due to the BB reaching maximum velocity inside the inner barrel (think of a AEG with a leaky O ring on a cylinder head). You have probably all seen an AEG that fires BB's about 10 meters due to some air leak or weak spring problem. This AEG's BB's would have started to deaccelerate well inside the inner barrel due to the velocity being low but the mass the same.

I've tried to steer clear of the Magnus effect as this is another force relative to velocity but would have a big impact on range. This hop, or rotational force, would add something to the overall momentum force at point of impact.

 

[GiantKiwi]

Why don't we shoot each other with steel BBs?

Being extremely facetious there.

Aside:

One of the sites that comes to mind is on the west coast, limits players to 0.25's, then forces you to chrono with not only 0.2's, but their 0.2's.

Actively inviting joule creep abusers to abuse it, and they do which is why i've not been back. 

But the limit on 0.25's is arbitrary, especially when it is very clear that those who set the rule, weren't following it whilst playing themselves.

 

[Adolf Hamster]

So bb's are not continuing to meaningfully accellerate once they've left the barrel.

The velocity it has when it passes a chrono, is going to be the maximum it has.

The joule creep thing is that for certain platforms, whilst heavier rounds result in lower velocity, its not proportional to the kinetic energy.

The difference is in constant pressure versus constant energy systems.

Lets say we have 2 cars at a drag strip, one heavier than the other.

The first run, we give them limited fuel. The lighter car has enough it can drive flat out the whole time and run out of fuel right as he passes the line. But the heavier car wether he drives flat out and coasts the last few hundred yards, or drives gentle so he runs out as he crosses the line either way he's going to be moving slower.

Thats your aeg, the fuel tank is your spring energy, you can fire a heavier round but it'll just go slower because the spring doesnt have any more to give.

Second run, the cars have unlimited fuel. Your lighter car puts in the same time as before driving flat out till he passes the line. The heavier car however, well now he can drive flat out the whole time and unlike last time he doesn't have to coast the last few hundred yards and keeps flat out. His car is heavier so he doesnt finish faster than the light car (remember kinetic energy factors in mass), but he beats his previous pass even though he's had to burn more fuel to get there.

This is your gbbr/hpa (at least the latter when tuned for heavier ammo), the gun during firing will just keep sending gas until the bb leaves the barrel, so if a heavier bb spends a bit longer in the barrel then it has more time to absorb the energy. In the case of lighter ammo, the unused "fuel" at the end of the race is the wasted gas that is still being supplied after the bb has left the barrel.

This is why the ratio between the weights, or the length of the barrel (the drag strip in our analogy) is a factor in this too. A pistol barrel isnt going to creep as much as a dragonuv, and the jump from 0.2 to 0.3 wont be as big as the jump from 0.2 to 0.4.

Limiting ammo weight is one way to lessen the effect, assuming people stick to it, but it aint as good as making sure that peoples pews, firing the ammo and settings they intend to use in-game, are within the acceptable limits.

 

[Tommikka]

On the matter of ‘joule creep’, as covered by most posters it is the change in muzzle energy that can result from firing a different projectile

(The earlier rocket example forgets to take into account that a rocket carries its energy source, therefore continues to accelerate due to the continuous propulsion

A BB flies down a barrel after an initial burst of energy combined with a cushion of air / gas pushing it up that barrel 

…………..

The hurty end when you get hit varies due to numerous factors, which include the rate at which energy drops away after leaving the barrel

A bigger BB has more surface area to go up against air resistence

A more dense BB could have the same surface area as a lighter less dense BB of an identical size

Back spin etc changes the way the projectile flies, it would be expected to fly further/straighter, but how it maintains its energy is a matter of conjecture and science 

I’ve seen systems that impart spin which gain longer/straighter flight, but then suddenly drop and at range have little impact (side spin can also result in shooting around objects if you have the skills and practice)

Impact sensors, additional chronographs, or high speed cameras could be used to measure velocity at different distances  

In ‘lethality’ testing ballistic gel is used to test the penetration upon impact 

 

[Rogerborg]

Being extremely facetious there.

Then it should be extremely trivial to remind us why we don't we shoot each other with steel BBs.

 

[GiantKiwi]

Then it should be extremely trivial to remind us why we don't we shoot each other with steel BBs.

Why keep bringing it up? Your point is null on this place, as we aren't using steel bb's. Inferring otherwise is just plain moronic.