Do you think getting shot with lighter BBs from an an upgraded gun would hurt more, less, or the same?

[mcguyver]

[Skladfin]

Originally Posted by mcguyver

Sorry, there is nothing incorrect in what I said.

Explain please why my M16A3 PTW will shoot 0.25g BB at 497 fps but will shoot a .20g at 530 fps? 20% decrease in BB mass but only a 6.6% increase in velocity? Don't worry, I already know the answer.

My old Marui G3 shot 265 with 0.25g and 295 with .20g. Same BBs (I haven't changed brands in years). Same 20% decrease in mass, but now an 11% increase in velocity.
.

that's a really dumb theory you have there, 20% decrease in mass doesn't mean 20% increase in velocity.

things don't work like that, it always have to follow a formula. We'll keep it simple, you can find the difference in velocity between 0.20g and 0.25g using 2 physics formulas

F= ma
vf(squared) = vi(squared) + 2ad

F = force applied
m = mass
a = acceleration
vf = Final velocity when leaving the barrel
vi = initial velocity before force being applied(so in this case, zero)
d = distance traveled between vi to vf

did some calculations and here are the results(In the calculation, I'm assuming that it fires 400FPS with 0.25g)
I also neglect any friction force between barrel and BB during barrel travel, and hop up effect.



From my chrono results(and yours too) shows that the difference in velocity between 0.20 and 0.25g IS roughly 40FPS give or take a few FPS (because of hop up/friction).

so no, 20% mass decrease in mass does NOT equal 20% increase in velocity.

[ujiro]

Keep in mind too if you took your gun with a mag with 0.20s, and then another with 0.25s, chances are the 0.20g bbs will be less affected by the hopup too. The 0.25s will push for longer, and push harder, upon the hopup then the 0.20s. I think so anyways.. lol.


EDIT: My point is that there are a lot of different things that come into play as to how much the speed will change when you change the BB weight.

[mcguyver]

Originally Posted by Skladfin

that's a really dumb theory you have there, 20% decrease in mass doesn't mean 20% increase in velocity.

things don't work like that, it always have to follow a formula. We'll keep it simple, you can find the difference in velocity between 0.20g and 0.25g using 2 physics formulas

F= ma
vf(squared) = vi(squared) + 2ad

F = force applied
m = mass
a = acceleration
vf = Final velocity when leaving the barrel
vi = initial velocity before force being applied(so in this case, zero)
d = distance traveled between vi to vf

did some calculations and here are the results(In the calculation, I'm assuming that it fires 400FPS with 0.25g)
I also neglect any friction force between barrel and BB during barrel travel, and hop up effect.



From my chrono results(and yours too) shows that the difference in velocity between 0.20 and 0.25g IS roughly 40FPS give or take a few FPS (because of hop up/friction).

so no, 20% mass decrease in mass does NOT equal 20% increase in velocity.

I know this. I was using the % as a measure of change, not an actual "to be expected" result. Re-read my post again.

[Skladfin]

Originally Posted by mcguyver

I know this. I was using the % as a measure of change, not an actual "to be expected" result. Re-read my post again.

then why did you even say such a thing.... it proved like.... nothing.

[mcguyver]

Originally Posted by Skladfin

then why did you even say such a thing.... it proved like.... nothing.

But it did. If you read it, you'd see that the change should be uniform, if theory actually translates to practice. Clearly it doesn't, as there are variables that are not factored in to a simple mass/energy/velocity equation.

Guns are too inconsistant to apply a simple formula and expect to get the right answer all the time. Sometimes it works, but that's luck.

[Flatlander]

Neat FYI: http://www.airsoftcanada.com/showthread.php?t=51752

I took every chrono reading in that thread, threw them into Excel and worked out the energy for each, then averaged them for each BB weight and data set. I posted my conlusion somewhere here but the jist of it was that as you increase your BB weight, the total kinetic energy (minus rotational) increased by around 5% for the same gun - EXCEPT the .28's always wanted to decrease slightly for some reason.

The pain vs weight question is also something that has boggled my mind. With a quick test we were doing one day we took a 400fps gun and a 370fps gun and tested them at around an average to long typical airsoft engagement distance (probably around 100+' but I'm terrible with distances). The .25's on the 400fps gun hit noticeably harder and the .23's on the 370fps gun hit noticeably harder. Probably around a dozen shots or so with each weight at each fps and on the legs

Ever since I did that test, I've been skeptical and want to do some more maybe this winter or next season (note, test was also confirmed by a buddy as we took turns shooting each other).

I'd like to hear someone who knows what they're talking about talk about pain and what factors are involved. I don't think simply saying KE without any proof or reason is good enough; the body is a pretty complex system.

There's also this to look over: http://cybersloth.org/airsoft/trajectory/index.htm

I looked over his theory and it seemed pretty sound (I had a few qualms) however his lack of empirical evidence (which he claims he has) to back up his neat little theory was sketchy. Seemed to me like a typical engineer...if it doesn't fit your theory, you fudge things to make it look like you know what you're talking about so you don't appear to be wrong.

[ujiro]

Originally Posted by mcguyver

But it did. If you read it, you'd see that the change should be uniform, if theory actually translates to practice. Clearly it doesn't, as there are variables that are not factored in to a simple mass/energy/velocity equation.

EVERYTHING THING IS too inconsistant to apply a simple formula and expect to get the right answer all the time. Sometimes it works, but that's luck.

Fixed for you.

[Itom]

Originally Posted by Azuki

Thats really cool. Where do you find stuff like that?

Not hard. Just enter the kinetic energy formula into excel spreadsheet.

What would be more impressive if you take into account air resistance at different temperatures.

[Qlong]

I'd say heavier BBs inflict more pain.

Reason being that heavier BB tend to be more dense than lighter BBs assuming both BB are composed of the same material, the latter being less packed, microscopic pockets of air should absorb more energy than a heavier BB with a higher density. Less pockets of air will give you a better transfer of energy without energy being absorbed by the material itself.


Movies would be so much more interesting if we didn't take physics.

[FOX_111]

Originally Posted by mcguyver

I think your graph is incorrect.

450fps with .20g should give 1.88j at the musle. So I guess other stats are also wrong.

I have good graphes somewhere that show everything you need to know about BBs ballistic, but it's not hosted on my server.

Edit: After closer inspection, the graph look fine. It's not very acurate, but it look fine. I retract my statements. But 450fps with .20g is still 1.88j.

That being said. Higher velocities with heavyer BBs require longer minimal engagement distances.
A 350fps (chronied with .2g) AEG require a minimal engament distance of 10fts using .25g in order to have 1j at impact.
Compared to a stock gun, 280fps with .2g require no MED since there is only about 0.7j at the musle.
Compared to these velocities.
400fps with .2g require a MED of 20fts using .25g BBs
450fps with .2g require a MED of 40fps using .30g BBs

So yeah, heavyer BBs punch harder and require longer MED.

[Styrak]

I think you're reading it wrong. It says 450fps is almost exactly 1.88J with .20's

[Schlyder]

That's how I see it too, 450fps with .20s is approx. 1.88J give or take .01J

[MadMax]

I would think that at close ranges pellet mass would not affect the damage/pain potential of an AEG. AEGs have shown themselves to be constant energy devices endowing a pellet with a consistent amount of kinetic energy despite varying pellet mass.

However I've found that the first 20' of flight can incur a significant velocity loss, especially with lighter pellets (shooting at a chrony at range).

I suspect that this is due to two causes:

-air resistance roughly varies with the square of velocity
-lighter pellets have lower energy density in terms of Joules/(fps)

A lighter faster pellet will experience significantly higher air resistance to a slower heavier (equivalent energy) pellet. That increased energy loss due to higher squared velocity will be compounded by the greater fps reduction when the pellet sheds kinetic energy from it's lighter body.


I have found GBBs and NBBs of many types to be significantly non constant energy devices, especially if they are propelled by a 2 phase compressed liquid-gas method (propane or HFC134a). I suspect that this is due to several factors:

-Higher initial pressures
-Higher gas density (propane (1.5x higher) and especially HFC134a (3.5x) have higher density than air)
-More complex pneumatic arrangement

Room temperature saturated propane exerts around 115psi. Conversely an AEG springs peak force results in a pressure of only 20psi (guesstimate based on the spring exerting 15lbf at full draw). The considerably higher pressure will experience a much higher initial flow rate which will incur much higher pressure losses over the convoluted pneumatic arrangement typical to most gas powered guns. I surmise that flow rate dependent pressure drops over the various valves and openings cause a considerable loss of pressure applied to the pellet.

For awhile I bashed my head against the question why such a high pressure didn't result in deadly velocities. If an AEG spring exerted such a small pressure in comparison to the saturated gas pressure of propane, why weren't propane guns dangerous?

First off, long barreled propane propelled rifles can exert very high velocities (500+ fps easily). Secondly, a magazine contained a relatively limited volume of pre expanded gas. Propane requires significant energy to boil off and maintain mag pressure so I suspect that the phase of pellet propulsion relies almost completely on the expanded gas.

This fixes the supply of gas phase propellant so you don't get a tremendously fast BB because the pressure starts to rapidly drop as gas expands through the gun and experiences pressure drops over all the various valves and orifices.

Propane and HFC134a have significantly higher density than air. Heavier gases experience higher pressure drops over flow resistances which will reduce the final pressure applied to a pellet. These pressure drops over flow resistances (valves and ports) will be dependent on the flow rate of the gas and apparent backpressure provided by the pellet. This means that the gas flow rate out of a gun is significantly dependent on the resistance to gas flow that a pellet presents. Therefore the pressure drops over various flow resistances will be ultimately pellet dependent.

I surmise that a funny issue of series resistance to gas flow situation arises in a gas airsoft gun. You start with a high initial pressure in the mag until the mag fire valve opens. Gas flows through the fire valve and mag rubber and nozzle body until it impinges on the back of the bb and starts it moving. Pressure builds up behind the pellet and gets it moving.

Even if the gas is dense compared to air, it's definitely not dense compared to the pellet so the gas flow starts to become dependent on how fast the pellet presently moves in the barrel.

I suspect that the pellet represents a resistance to gas flow which is in series with all of the other orifice resistances. Heavier pellets represent higher resistances to flow while lighter (faster accelerating pellets) represent a lower resistance.

This is the bit for DonP: This presents a funny series resistance situation analogous to an electrical series resistance where a fraction of power is dissipated over all of the series resistances. For the most efficient power delivery to the intended load (the pellet, or analogous motor in your circuit) you should maximize the resistance of the intended load to put most of the pressure (or analogous voltage) drop at your intended load.

In the case of lighter pellets, the pellet moves fast enough that it allows a higher flow which incurs higher pressure drops over the orifices and valves resulting in lower pressure applied to the pellet. Less pressure means less force for given distance which means less muzzle energy. Heavier pellets slug down the flow rate and put more of the pressure drop at the pellet which means higher muzzle energy.

[Schlyder]

So the heavier BB gets a bigger kick in the pants, because it allows the pressure that's built up behind it to be usable, and maximize efficiency. Where the lighter BB doesn't use the pressure build up behind it efficiently, and there is pressure loss through leaks in the mechanism before it can be used by the projectile. That all makes sense to me.
I am visualizing a water hose with water flowing out. You put your thumb over the end for just a second, and then release it and there is an increase in the flow from built up pressure. If you hold your thumb there again,but for longer this time, the pressure build up is greater, so when you release the flow again, the water will travel farther and faster.