.20 or .25?

bazinga733 · Jul 12, 2016

I am planning on buying a G&G CM16 Raider, that chronos at around 330 - 350 FPS with .20 gram BBs. However, I would prefer to use .25s due to their greater accuracy. Could I do this? Or will my FPS drop too low?

I plan on playing in an outdoor field with the maximum range I would have to fire through being around 75 - 100ft.

Thanks for any advice!

MNairsoft7 · Jul 12, 2016

Use .25. They may move a little slower, but it will travel a longer distance and be much more accurate.

Also look op some easy hop up mods, those will also increase accuracy and range.

Spaceman7 · Jul 12, 2016

Well, 20 FPS is quite a bit of fluctuation, about (roughly) the same amount you'll lose by switching to .25s. The accuracy will be a noticeable improvement, though, depending on the brand of the BB. Especially when playing outdoors, heavier weighted BBs really shine when countering any sort of wind.

I would say try to play with .25s, but if for some reason you don't like them (you probably will), you can just switch back to .20s.

For instance, I run .30s in my DMR/R-Hopped/Long Barreled guns, .25s in my standard field/cqb guns, and .20s in my pistols/SMGs (where accuracy/range won't quite matter).

I also use .20s in any guns I loan out because I've learned the people I give Hi-Caps to like to burn through my $30 bags of .30 Biovals in two games. They now get to use my crappy .20s because they don't care to understand trigger discipline at all.

Raven1st · Jul 12, 2016

There was a really good study done on BB weights several years ago, I need to go back and find my bookmark but it was a great resource into the behavior of BB flight.

Edit:
Airsoft Trajectory Project.

http://mackila.com/airsoft/atp/

Spaceman7 · Jul 12, 2016

Raven1st said:
There was a really good study done on BB weights several years ago, I need to go back and find my bookmark but it was a great resource into the behavior of BB flight.

Edit:
Airsoft Trajectory Project.

http://mackila.com/airsoft/atp/

Those graphs are pretty much saying that a heavier BB has an advantage in every scenario, even ToT (Time on Target), even though they are fired at a slower initial velocity.

Pls explain? Is the drag coefficient smaller on a more massive object of the same dimensions?

Raven1st · Jul 12, 2016

It has to do with conservation of energy.
This is the part where I get iffy with my knowledge with physics, but a heavier object will hold onto the energy it has better than lighter object of the same dimensions.
This means that while a lighter object will have a higher velocity for any given energy when compared to a heavier object it will loose the velocity much faster, so at range it will be traveling slower than a heavier object of the same dimensions.

Spaceman7 · Jul 12, 2016

Raven1st said:
It has to do with conservation of energy.
This is the part where I get iffy with my knowledge with physics, but a heavier object will hold onto the energy it has better than lighter object of the same dimensions.
This means that while a lighter object will have a higher velocity for any given energy when compared to a heavier object it will loose the velocity much faster, so at range it will be traveling slower than a heavier object of the same dimensions.

Time for a little physics, then:

BB Characteristics:

Radii
BBr1: 5.98mm = 0.00598m
BBr2: 5.98mm = 0.00598m

Masses
BBm1: .20g = .002kg
BBm2: .25g = .0025kg

Velocity
BBv1: 400 f/s or 121.92 m/s
BBv2: 358 f/s or 109.12 m/s

Coefficient of drag for a sphere is .47
We'll just use air density as a unit of 1kg/m^3, for simplicity

Calculating Cross-Sectional Area:
BBsa1: pi*r^2 = pi*.00598^2 = 0.000112m^2
BBsa2: pi*r^2 = pi*.00598^2 = 0.000112m^2

Calculating Drag Force:
Where csa = cross-sectional area, rho = air density, cd = coefficient of drag.

BBdf1: 0.5*v^2*csa*rho*cd = 0.5*121.92^2*0.000112*1*0.47 = .391N
BBdf2: 0.5*v^2*csa*rho*cd = 0.5*109.12^2*0.000112*1*0.47 = .313N

Calculating Deceleration of the BB
F=ma, where F = force, m = mass, and a = acceleration. Rewrite as a=F/m.

These are negative values because it's acceleration in the negative direction:

BBa1: a = F/m = .391/.002 = -195.5 m/s^2
BBa2: a = F/m = .313/.0025 = -125.2 m/2^2

This is deceleration in the plane opposite the velocity vector, since all objects decelerate (or accelerate downwards) at a rate of 9.8 m/s^2 due to gravity (the y-plane).

The difference seems somewhat negligible in distances as small as 200 feet (60.96 meters)...

Now, projectile motion with the inclusion of air resistance delves into differential equations, and while I've been through the course, I don't feel like diving into it at midnight on a Monday night. My classes don't start for another month or so and I've already done much too much math tonight. So, I downloaded a program that would run it for me, because today is the future and we can do stuff like this. Below are the results (1.7m is the average height of a man, assuming firing at a target at an equal altitude):

.20:

.25:

The .20 covered 54.36 meters in .65 seconds, giving it an average velocity of: 83.63 m/s or 274.38 f/s.
The .25 covered 52.00 meters in .63 seconds, giving it an average velocity of: 82.54 m/s or 270.80 f/s.

At this distance (~175 feet), given the velocities from that website (400fps at .20 = 358fps at .25), the .20 wins for time on target.

I'm not satisfied:

I messed with the initial height until I had both the BBs landing about ~90 meters away from the starting point, which is right around the 300 foot mark, where all of these pro-DMR-ers claim to be reaching out to (and it is possible). Of course, this program can't simulate hop-up, but this is just a BB weight battle, not including hop-up effects.

.20:

.25:

The .20 covered 89.68 meters in 1.42 seconds, giving it an average velocity of: 63.15 m/s or 207.19 f/s.
The .25 covered 89.97 meters in 1.38 seconds, giving it an average velocity of: 65.20 m/s or 213.91 f/s.

The .25 starts to overtake the .20 at distances around ~70-80 meters, I believe. I could find the exact number by calculating the intercept, but no thanks.

*FUN FACT* Without air resistance, we'd be able to shoot about 25% further, at the distances we usually play at.

TLDR: The difference in the velocity of the round doesn't matter nearly as much as we all think it might, since the lighter rounds are affected by drag more than the heavier rounds. You are better off using a heavier round, since on top of a very, very, very, very small drawback of time on target (that actually becomes better than lighter BBs, the further you are shooting), you get better accuracy and much better wind resistance. Use heavier BBs.

Enough physics, calculus, and math in general for Spaceman tonight.

TheInfidel23 · Jul 12, 2016

Just use .25's, you'll greatly appreciate the added accuracy and range they offer, and the speed difference will be negligible to your eye.

Raven1st · Jul 12, 2016

-slow clap-

The only thing all your math is missing is the terminal velocity, which makes a huge impact on range.

I use .30g because that's what all my GBB's like and it keeps a fair amount of velocity down range.
I have noticed a significant improvement in performance over .25's when using .30's, mostly in how much leeway I have in the hopup, and they just seem to run better in my GBB's overall so I use them.

I didn't really use science to pick them.

Iram · Jul 14, 2016

Spaceman7 said:
Time for a little physics, then:

BB Characteristics:

Radii
BBr1: 5.98mm = 0.00598m
BBr2: 5.98mm = 0.00598m

Masses
BBm1: .20g = .002kg
BBm2: .25g = .0025kg

Velocity
BBv1: 400 f/s or 121.92 m/s
BBv2: 358 f/s or 109.12 m/s

Coefficient of drag for a sphere is .47
We'll just use air density as a unit of 1kg/m^3, for simplicity

Calculating Cross-Sectional Area:
BBsa1: pi*r^2 = pi*.00598^2 = 0.000112m^2
BBsa2: pi*r^2 = pi*.00598^2 = 0.000112m^2

Calculating Drag Force:
Where csa = cross-sectional area, rho = air density, cd = coefficient of drag.

BBdf1: 0.5*v^2*csa*rho*cd = 0.5*121.92^2*0.000112*1*0.47 = .391N
BBdf2: 0.5*v^2*csa*rho*cd = 0.5*109.12^2*0.000112*1*0.47 = .313N

Calculating Deceleration of the BB
F=ma, where F = force, m = mass, and a = acceleration. Rewrite as a=F/m.

These are negative values because it's acceleration in the negative direction:

BBa1: a = F/m = .391/.002 = -195.5 m/s^2
BBa2: a = F/m = .313/.0025 = -125.2 m/2^2

This is deceleration in the plane opposite the velocity vector, since all objects decelerate (or accelerate downwards) at a rate of 9.8 m/s^2 due to gravity (the y-plane).

The difference seems somewhat negligible in distances as small as 200 feet (60.96 meters)...

Now, projectile motion with the inclusion of air resistance delves into differential equations, and while I've been through the course, I don't feel like diving into it at midnight on a Monday night. My classes don't start for another month or so and I've already done much too much math tonight. So, I downloaded a program that would run it for me, because today is the future and we can do stuff like this. Below are the results (1.7m is the average height of a man, assuming firing at a target at an equal altitude):

.20:

.25:

The .20 covered 54.36 meters in .65 seconds, giving it an average velocity of: 83.63 m/s or 274.38 f/s.
The .25 covered 52.00 meters in .63 seconds, giving it an average velocity of: 82.54 m/s or 270.80 f/s.

At this distance (~175 feet), given the velocities from that website (400fps at .20 = 358fps at .25), the .20 wins for time on target.

I'm not satisfied:

I messed with the initial height until I had both the BBs landing about ~90 meters away from the starting point, which is right around the 300 foot mark, where all of these pro-DMR-ers claim to be reaching out to (and it is possible). Of course, this program can't simulate hop-up, but this is just a BB weight battle, not including hop-up effects.

.20:

.25:

The .20 covered 89.68 meters in 1.42 seconds, giving it an average velocity of: 63.15 m/s or 207.19 f/s.
The .25 covered 89.97 meters in 1.38 seconds, giving it an average velocity of: 65.20 m/s or 213.91 f/s.

The .25 starts to overtake the .20 at distances around ~70-80 meters, I believe. I could find the exact number by calculating the intercept, but no thanks.

*FUN FACT* Without air resistance, we'd be able to shoot about 25% further, at the distances we usually play at.

TLDR: The difference in the velocity of the round doesn't matter nearly as much as we all think it might, since the lighter rounds are affected by drag more than the heavier rounds. You are better off using a heavier round, since on top of a very, very, very, very small drawback of time on target (that actually becomes better than lighter BBs, the further you are shooting), you get better accuracy and much better wind resistance. Use heavier BBs.

Enough physics, calculus, and math in general for Spaceman tonight.

The front page says they're looking for authors. You might want to submit that.

Violet_Shift · Jul 15, 2016

This seems enough to persuade me to go up to 0.3's for my SCAR DMR. Been using .25's since they're what my field supplies and my machine gun likes them. Might get myself a bag of ones for precision use.

Spaceman7 · Jul 15, 2016

Violet_Shift said:
This seems enough to persuade me to go up to 0.3's for my SCAR DMR. Been using .25's since they're what my field supplies and my machine gun likes them. Might get myself a bag of ones for precision use.

Glad to be of service.

The fact that the difference in time on target is within a tenth of a second at a common engagement range (150 feet), it's pretty safe to say heavier weights are typically better.

Multi-quote is hard on a phone, so to the guy that suggested I sign up for the authoring, thank you much for the recommendation. I'll run it by and see what comes of it. Maybe a sticky thread, or something.

SinisterSteve · Dec 30, 2016

I would go with the the .25s as well man. The trade off will be worth it. The drop in fps is worth the increase in accuracy. And as spaceman said the wind won't carry the bb as much as a .20. just remember it'll be harder to hit a moving target at range considering it will take your bb longer to get there

.20 or .25?

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