Need buying advice!!!

[arock1214]

Ok so I'm looking to buy an airsoft gun that goes 375 fps or under with .25g bbs for $130 or less. Any recomendations? Please post!  [smilie=armata_pdt_04.gif]

[Henriksenator]

It is pretty much impossible to find a gun that shoots that fast for that cheap. You could buy a used gun and then just put in a m120 spring into it.

[Pick]

He's right its impossible to get that new without giving up something

However here's a sales pitch I got a MP5 that is shooting 400 with .20s for 125$ I will give you a m110 spring to go with it that would drop down to 375 with .20s it has a m4 length barrel in it and is full metal it would also come with 3 hi caps and a 9.6v 1500mah battery wired for deans

[DMAN007]

He's right its impossible to get that new without giving up something

However here's a sales pitch I got a MP5 that is shooting 400 with .20s for 125$ I will give you a m110 spring to go with it that would drop down to 375 with .20s it has a m4 length barrel in it and is full metal it would also come with 3 hi caps and a 9.6v 1500mah battery wired for deans

I'd buy that if I was you...

[armalite attack]

He's right its impossible to get that new without giving up something

However here's a sales pitch I got a MP5 that is shooting 400 with .20s for 125$ I will give you a m110 spring to go with it that would drop down to 375 with .20s it has a m4 length barrel in it and is full metal it would also come with 3 hi caps and a 9.6v 1500mah battery wired for deans

400 with .2's is around 360 with .25's so I don't think you need to even add the spring.

[Pick]

He's right its impossible to get that new without giving up something

However here's a sales pitch I got a MP5 that is shooting 400 with .20s for 125$ I will give you a m110 spring to go with it that would drop down to 375 with .20s it has a m4 length barrel in it and is full metal it would also come with 3 hi caps and a 9.6v 1500mah battery wired for deans

400 with .2's is around 360 with .25's so I don't think you need to even add the spring.

Yeah that's true still I tossing the spring in with it

[rmwilson90]

400 with .2's is around 360 with .25's so I don't think you need to even add the spring.

You still get the same energy output though, so you're not being any safer using heavier BB's. I'm assuming the fps limit he's looking at ( <375 ) is because he'll be doing CQB? Correct me if I'm wrong.

[Pick]

400 with .2's is around 360 with .25's so I don't think you need to even add the spring.

You still get the same energy output though, so you're not being any safer using heavier BB's. I'm assuming the fps limit he's looking at ( <375 ) is because he'll be doing CQB? Correct me if I'm wrong.

That is true energy will still be the same but the way he wrote it he is looking for something at that fps with .25s

[rmwilson90]

That is true energy will still be the same but the way he wrote it he is looking for something at that fps with .25s

Oops, you're right, he did, lol. I completely overlooked it  ](*,)

[Pick]

That is true energy will still be the same but the way he wrote it he is looking for something at that fps with .25s

Oops, you're right, he did, lol. I completely overlooked it  ](*,)

Lol its all good the gun I am selling is a good deal within his range and has a longer barrel

[Whiskey11]

400 with .2's is around 360 with .25's so I don't think you need to even add the spring.

You still get the same energy output though, so you're not being any safer using heavier BB's. I'm assuming the fps limit he's looking at ( <375 ) is because he'll be doing CQB? Correct me if I'm wrong.

That is true energy will still be the same but the way he wrote it he is looking for something at that fps with .25s

Unless you've spent the time to tune your system to use .20's with volumes, etc... there is no way that a .20 and .25 will carry the same energy.  Simply wont happen.  There is a lot of physics to this, but if you chrono your AEG with .20's (ten shots lets say) then figure out the respective energy level of each shot and average it out, then do the same with .25's, you'll be surprised that a .25 may carry more energy in your AEG.

I'll use my G&G M14 Veteran as an example.  My Vet chronoes around 455 w/ .20's, but 390 w/ .28's.  The Muzzle energy of the .20's is aprox 1.92 Joules where as with .28's it is 1.98 Joules.  

In Black Fox's thread about his Golden secret or whatever, I went into more detail about this.

Just thought I'd give you all the heads up though

[rmwilson90]

400 with .2's is around 360 with .25's so I don't think you need to even add the spring.

You still get the same energy output though, so you're not being any safer using heavier BB's. I'm assuming the fps limit he's looking at ( <375 ) is because he'll be doing CQB? Correct me if I'm wrong.

That is true energy will still be the same but the way he wrote it he is looking for something at that fps with .25s

Unless you've spent the time to tune your system to use .20's with volumes, etc... there is no way that a .20 and .25 will carry the same energy.  Simply wont happen.  There is a lot of physics to this, but if you chrono your AEG with .20's (ten shots lets say) then figure out the respective energy level of each shot and average it out, then do the same with .25's, you'll be surprised that a .25 may carry more energy in your AEG.

I'll use my G&G M14 Veteran as an example.  My Vet chronoes around 455 w/ .20's, but 390 w/ .28's.  The Muzzle energy of the .20's is aprox 1.92 Joules where as with .28's it is 1.98 Joules.  

In Black Fox's thread about his Golden secret or whatever, I went into more detail about this.

Just thought I'd give you all the heads up though

Aha, I wasn't actually aware of that. I'd read somewhere else that "using heavier BB's, while reducing FPS, does not reduce muzzle energy" (quotes used lightly). I took this to mean that it stayed the same, conservation of energy and all that, thanks for the info!

[Whiskey11]

400 with .2's is around 360 with .25's so I don't think you need to even add the spring.

You still get the same energy output though, so you're not being any safer using heavier BB's. I'm assuming the fps limit he's looking at ( <375 ) is because he'll be doing CQB? Correct me if I'm wrong.

That is true energy will still be the same but the way he wrote it he is looking for something at that fps with .25s

Unless you've spent the time to tune your system to use .20's with volumes, etc... there is no way that a .20 and .25 will carry the same energy.  Simply wont happen.  There is a lot of physics to this, but if you chrono your AEG with .20's (ten shots lets say) then figure out the respective energy level of each shot and average it out, then do the same with .25's, you'll be surprised that a .25 may carry more energy in your AEG.

I'll use my G&G M14 Veteran as an example.  My Vet chronoes around 455 w/ .20's, but 390 w/ .28's.  The Muzzle energy of the .20's is aprox 1.92 Joules where as with .28's it is 1.98 Joules.  

In Black Fox's thread about his Golden secret or whatever, I went into more detail about this.

Just thought I'd give you all the heads up though

Aha, I wasn't actually aware of that. I'd read somewhere else that "using heavier BB's, while reducing FPS, does not reduce muzzle energy" (quotes used lightly). I took this to mean that it stayed the same, conservation of energy and all that, thanks for the info!

In a frictionless world and tolerances that approach zero milimeters and an Ideal world, Conservation of energy can apply, unfortunately, the average BB is 5.95-5.98mm and the average bore of a barrel is 6.03 (Ok, maybe not average, but you get my point).  There is a lot of space there.  Then you have to factor in that air is compressable, heavier BB's stay in the barrel longer, etc etc.

To a point, heavier BB's will have a higher muzzle energy than a lighter BB, and then it will fall off.  My Veteran, again is an example of that, it climbs through to .28's, stays constant through .30's, then .36 and heavier are all less muzzle energy again.  

We are not an ideal world, and our systems are far from efficient at propeling a BB down a barrel, and so ideal physics equations rarely work out terribly well when looking at the big picture.  The Micro Level (IE: Muzzle energy being 1/2*mass*velocity^2) ideal equations are ok, but not 100% accurate either.

[axisofoil]

It's usually no more than a 5-10% maximum difference. But it is a difference. .5*m*v^2 doesn't work because of hop-up. Different weight of bb needs a different amount of backspin to create the same hopup effect... and energy goes into that. They have to generate a different amount of lift, is why there's a difference. heavier bb's have to have more spin applied... so if you ended up working it out (I refuse to do so), you have a much larger increase in energy output if your linear output (.5*m*v^2) is within 5-10% of the other weights.

You will also see much bigger distances down-range though. Slower moving bb has less drag and therefore less frictional losses. So at the same range, a heavier bb will more likely still be carrying more energy.

Then you have to consider all the effects that whiskey mentioned.

Then you have to add in randomized occurances.

Or you can just do the rule of thumb measurements we take... fps should be ____ or less with ___g bb's.

[Crono0001]

It's usually no more than a 5-10% maximum difference. But it is a difference. .5*m*v^2 doesn't work because of hop-up. Different weight of bb needs a different amount of backspin to create the same hopup effect... and energy goes into that. They have to generate a different amount of lift, is why there's a difference. heavier bb's have to have more spin applied... so if you ended up working it out (I refuse to do so), you have a much larger increase in energy output if your linear output (.5*m*v^2) is within 5-10% of the other weights.

You will also see much bigger distances down-range though. Slower moving bb has less drag and therefore less frictional losses. So at the same range, a heavier bb will more likely still be carrying more energy.

Then you have to consider all the effects that whiskey mentioned.

Then you have to add in randomized occurances.

Or you can just do the rule of thumb measurements we take... fps should be ____ or less with ___g bb's.

Axisofoil is right about the rotational energy and drag.  There's going to be a lot of drag, unless you're shooting in the vacuum.  Drag is a function of velocity of the bb, which in turn is a function of the mass of the bb.  The actual kinetic energy curve vs. mass is going to be a curve that can be optimized.  If you would like to,

Total Energy in X Direction = Kinetic Energy - Rotational Energy - Drag

E = .5mv^2 + .5Iw^2 + .5vpCA

I = moment of inertia, spheres having (2/5)mr^2


So substituting it back in,

E = .5mv^2 + (1/5)mr^2w^2 + .5vpCA

Where
m = mass
v = velocity
r = radius of the sphere
w = angular velocity
p = density of air
C = drag coefficient, dependent on shape (spheres are about .47)
and A = projected area, a bb being a circle when it hits the air

So what you could do is measure how fast you shoot with each BB, plot the energy as a function of mass and velocity, and then you could optimize that curve for the maximum amount of energy by simply taking its derivative and setting it equal to zero.  You got two variables so you'll need to do partials.

Actually, if you wanted to avoid partials, what you could do is plot velocity vs. mass, and fit a regression to that (something tells me it's going to be first or second order... simple), take that function and then substitute it into that energy equation I gave you for E.  Then you have one big equation for energy in terms of mass or velocity (you choose), and you'd just take the first derivative.  It cannot be worse than a fourth order equation, which means that you may have two maxima.  Just find whichever one is larger and use that one for more energy.

Not difficult at all.