GBBR weirdness

[Zaphod]

I just got my new WE GBBR (M16A3) the other day and set the valve to 420fps on .2s. Since i'm running .3s i thought id chrono it on them. The weird thing was it was still doing the same speed. Tried .28s and got the same speed.

At my first game with it i checked it at lunch time (its summer here and its stupidly hot) and it was still doing 420 on .2s.

Its not really a problem but just a bit confusing/interesting. Any one know why or had a similar problem?

[Sacre]

Actually, the .2's, and the .3's, will exit the barrel at the same speed. But, the .3's will continue to maintain a higher speed for a longer period of time then the .2's. So this will result in more accuracy, etc. The lighter the BB, the more it will be affected by wind resistance, etc.

So the .3's won't give you more speed, it'll just give you a longer distance, and better accuracy than the .2's.

So i don't see an issue here :P

If i'm wrong anyone, by all means correct

[Huron]

Nope, .3's should give him less speed, because it's the output energy that stays constant. So for the energy to be constant with an increased projectile mass means the velocity is lowered because it takes more energy to get a .3 to the same speed. This isn't dead on for gas guns though, because of the expanding gas in the barrel exerting more force on heavier BB's for some reason or another. The hardcore gas gun lovers/engineering pros can explain how that works lol.

That being said, he should be experiencing a bit of an FPS loss when switching to .28's and .3's. So not factoring in the weird effect of using compressed gas, 420ft/s on .2's should give about 340ft/s on .3's. So I don't know what's up with the rifle, maybe the chrono is off?

[Zaphod]

It might be the chrono but i tested heaps of other guns that day and it was reading fine. Used a different chrono at todays game too. Maybe i was just lucky with the rifle

[Huron]

I found a little bit of information here. Nothing specific, but it's post number 7 in this thread:
http://www.airsoftcanada.com/showthread.php?t=94517

There might be more on it further along there. If you don't find anything I recommend PM'ing someone here who knows their stuff about GBBR's, ILLusion and m102404 are two that come to mind.

[m102404]

What you observed is normal...try 0.25's and you'll probably get around the same velocity.

Gas systems are not the same as spring powered systems...unlike an AEG where the amount of force is constant, with a gas system there are more variables in play.

The way the gas system works is that the BB has to exit the barrel before the recoil portion starts. How much gas is dumped down the barrel and how quickly the recoil phase starts adjusts the resultant FPS. Redwolf has a good write up on GBB systems...just picture that but bigger for your rifle.

Long barrels, lots of gas = high velocity

Long barrels have the "room" for gas to expand (where as pistol barrels are really too short to let this happen fully and you'll see more of a variation for different BBs).

[ILLusion]

This is exactly why game hosts SHOULD be operating their games with a maximum WORK (JOULE) OUTPUT LIMIT, rather than an FPS limit.

I won't explain WHY it's doing this, as m102404 already covered this above, but I'm going to discuss what this means to you.

With spring and electric systems, the conversion is constantly linear. Meaning, regardless of how heavy your BB is, the work output level will ALWAYS be constant. If it shoots 1 Joule with a 0.2g BB (328fps), it will also shoot 1 Joule with a 0.36g BB (245fps). At the muzzle, the amount of pain felt by the target will remain exactly the same.

However, with a gas gun, if you set your gun to shoot and chrony 420fps with 0.2g (1.63 Joules) and proceed to head on to the field with 0.3g BBs shooting 420fps, you'll be shooting 2.45 Joules. To put that in to a number that you may understand better, you would be effectively shooting your targets with what is equivalent to 515fps with 0.20g BBs (at the muzzle.)

Also, because of the ballistic nature of heavier projectiles, they will carry that higher muzzle energy a lot further down range than lighter ammunition will. The end result is a dramatically increased damage level inflicted to your target.

That is causing unnecessary hurt and damage to your opponents... pain that I'm sure they WON'T appreciate.

Tune your gun for the ammo load you will be using, and don't deviate, for safety reasons. Breach of safety and consciously setting your gun to set it to such harmful levels is reason for any game host to ban you from a field.