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BB weight vs. fps drop *rough* testing

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Old December 19th, 2007, 22:58   #1
CDN_Stalker
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BB weight vs. fps drop *rough* testing

Testtube came by tonight to discuss stuff and business (as well as drop off a bag of 0.20g and 0.25g Bastards as gifts to me.......... is good to be in partnership with the local Bastard!) and he and I did some rough chrony results with my new F1 Chrony and my CA M24 (Laylax/First Factory 150SP spring, used for 2 solid years and showing wear, Guarder 9mm bearing spring guide, Guarder piston and piston head, Prometheus 6.03mm tightbore barrel and RH65 hop up rubber) to see what differences BBs from 0.20g to 0.43g BBs had in relation to each other (about a foot away from the chrony). Since I'm running really low with the Straight 0.36g and 0.43g BBs, we only tested three shots of each, got an average and sorted out the differences in weight vs. fps drop. I figured this might prove interesting to some, and also gives rough estimate of fps if a gun is chronied with 0.20g BBs but the user wants to know about what 0.25g or 0.28g BBs might sit at in use from the muzzle.

BB Bastards:

0.20g

468.8
457.1
467.9
Average: 464.6fps

0.25g

429.9
425.3
430.2
Average 428.46fps

0.28g

397.9
403.0
400.1
Average 400.33fps

SIIS

0.30g

394.4
392.3
389.3
Average 392.00fps

Straight:

0.36g

359.7
366.9
355.8
Average 360.8fps

0.43g

336.2
340.3
335.2
Average 337.23

So, what we have for differences between weights (velocity vs. weight difference)is:

0.20g @ 464.6fps
\
}-36.14fps for +0.05g
/
0.25g @ 428.46fps
\
}-28.13fps for +0.03g
/
0.28g @ 400.33fps
\
}-8.1fps for +0.02g
/
0.30g @ 392.0fps
\
}-31.2 for +0.06g
/
0.36g @ 360.8fps
\
} -23.57fps for +0.07g
/
0.43g @ 337.23fps

Hope this provides some useful info, even if it's just basic stuff (again the word rough pops up, but seems a trend to count on for rule of thumb guessing is 10fps decrease in velocity for every 0.02g difference in BB weight increase.)

PS: Gonna post this around, so don't be surprised to see it elsewhere.

Last edited by CDN_Stalker; December 19th, 2007 at 23:04..
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Old December 21st, 2007, 20:05   #2
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Hmm, tough audience.
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Old December 21st, 2007, 20:14   #3
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Thanks for the info. 0.25 seems like the best to go with.
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Old December 21st, 2007, 20:26   #4
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Actually 0.28g is the best to go with if you have a gun shooting over 350fps, under that 0.25g. 0.20g are useless for outdoors though, in any gun even stock (unless close and no brush or grass to shoot through).

Point of all this (excluding sniper rifles) is just to show the difference in fps between BB weights. Focus more on performance than velocity.
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Old December 21st, 2007, 21:07   #5
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Started using 0.28g in my M4 this summer (400fps). Will never ever go back to 0.25g with this setup.
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Old December 21st, 2007, 21:15   #6
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I think the comparison between the effect of different weights of BBs on Maximum range will be much more interesting and bring much more audience.
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Old December 21st, 2007, 21:19   #7
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I was thinking for what I primarily shoot in CQB, which are GBB's powered by Propane.
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Old December 21st, 2007, 21:26   #8
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I have a systema currently useing the 110 cylinder, Im wondering whats the best bb weight for range? I hear that lighter dosent = more range but I have no clue.
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Old December 21st, 2007, 21:31   #9
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I was just playing around with the numbers and it appears (from your data) that .28's are actually the 'worst'. Now this is coming from a purely numbers standpoint and from someone who hasn't personally used .28's, take into account Anyways here's what I came up with:

Kinetic Energy in Joules (excluding rotational energy obviously):

.20 - 2.005
.25 - 2.132
.28 - 2.084
.30 - 2.141
.36 - 2.177
.43 - 2.271

Notes:

-These are the kinetic energies (KE) averages calculated from each FPS reading you supplied above.

-There is a clear trend that as the mass increases, the KE actually increases SLIGHTLY - with the only exception of .28's. Think about this - your gun is able to transfer more KE into a BB's if there is more mass (neat!). Why? Well my theory is because the extra inertia (mass) will cause a higher pressure to be obtained behind the BB - as in it takes more time to move the BB so a slight increase backpressure is caused.

- Note that muzzle velocity is not the only factor in distance. Rotational energy must all be taken into account (AKA Hop-up / Bernoulli's principle). My guess is that with increased BB mass will result in less angular velocity (backspin).

-What does all this mean in a practical sense? Hell if I know!

A larger sample size as well as actual distances would be much more helpful! The low sample size might be the cause of the .28's not following the trend.

For those of you thought "WTF is a Joule?", here's some more calculation basically supporting the above. Below is the Difference in Velocity / Difference in Mass (with .2's used as the standard to compare the difference):

.25 - 722
.28 - 803.8
.30 - 726
.36 - 648.8
.43 - 549.1

-Note the trend is for the numbers to decrease - except for the .28's.

-There is no linear relationship between change in velocity and change in mass (ie. You almost double the mass - compared to a .2 - by using a .43g BB but you do not cut the velocity in half). Which is why energy comparison is used (KE = .5 X Mass X Velocity^2)

Last edited by Flatlander; December 21st, 2007 at 21:35..
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Old December 21st, 2007, 21:52   #10
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The BB's fps doesn't necessarily determine it's overall range, some guns shoot less hard and get more range, and since they lose their energy more slowly than some fast fps guns, you may be more likely to feel a hit from a long range gun. But that has to do with internal parts.
The mechanics are really complicated to me, but I find theres an optimal velocity at which bb's perform better. So although a .28 may have less fps and less kinetic energy than a .25, it's still harder for outside forces to knock it off its flight path and so it's more accurate and more likely to travel further. Whereas if you fire a .43 at 275fps (about 400fps on .2s), you can't put enough backspin velocity on it to keep it in the air for very long at that low speed.
Hope that makes sense lol
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Old December 21st, 2007, 21:53   #11
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Originally Posted by pawscal View Post
I have a systema currently useing the 110 cylinder, Im wondering whats the best bb weight for range? I hear that lighter dosent = more range but I have no clue.
0.28g for you.

Lighter BBs generally don't result in more range because their low weight means they are relatively bad at retaining momentum compared to heavier BBs. This is especially problematic when one considers the greater air resistence they encounter from their higher muzzle velocity.
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Old December 21st, 2007, 22:05   #12
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Old December 21st, 2007, 22:53   #13
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Okay so the 3 things that determine a BB's maximum range are:

1) Velocity

2) Backspin

3) Mass ('weight')

Now to actually work out what works best via numerical methods would be a nightmare and here's why:


Drag:
The coefficient of drag over a sphere DECREASES with increasing Reynold's number. The Reynolds number is determined by the velocity of the sphere/BB (along with other constants). So what does this mean: Shoot the BB faster and it will have a lower coefficient of drag which means more range (yay!)

However: the FORCE of drag is =0.5 X coefficient of drag X Area X Density of fluid (air) X Velocity^2 . So now what that means is the faster you shoot, the bigger the drag force is on the BB and note that the velocity is SQUARED. So what this means is that the faster FPS you have, the faster the BB will slow down INITIALLY...you will still get further distance in the end.

Mass and Velocity:
So the more mass you have the less the BB is affected by drag and outside forces like wind/brush (mass does not change anything about the actual drag forces - only there is more mass for these drag forces to act on). However, the more mass you have the less velocity you have.

Backspin/hop-up:
Okay so hop-up/backspin works on the Bernoulli principle. Basically the air travelling over the top of the BB is faster than the air travelling on the bottom of the BB. So this velocity difference creates a PRESSURE difference (low pressure on top, high pressure on bottom). So there is a new FORCE upwards (or 'lift' upwards) resulting in longer 'hang time'. Hence why we have hop-up on our guns. So now that we have a longer 'hang time' we want to maximize this by having the largest velocity possible over this time. However, as mentioned previously it is not a simple case of having the highest muzzle velocity (BB mass, coef of drag, etc come into play).

Okay, so now you need to have maximum backspin to increase this differential pressure and increase the hang time. So if you go to a heavier BB you will lose some of this backspin (Note: this is an educated guess!) and velocity.

So in conclusion:
How the hell am I supposed to figure out what works best then you ask! You're going to have to test, measure and play around to see what works best with your set up as everyones guns and hop-ups will perform differently.

Things to remember:

-Lighter BB means more FPS (more range), more backspin (more hang-time), is more affected by wind.

-Heavier BB means less FPS, less backspin, less affected by wind, *should* retain its velocity for longer (ie. velocity drop will be slower).

-Maximizing these things will be very tricky but obviously (IMO) you should focus on maximizing your hop-up to give you the most backspin, creating more 'hang time' for your BB. FPS at the muzzle is not the be all and end all for range!
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Old December 21st, 2007, 23:18   #14
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Anyone ever see a .2 bb go further than a .25? (serious question, not sarcasm)
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Old December 21st, 2007, 23:22   #15
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I've never actually measured or stepped it off but it *looked* like my .2's were going further than my .25's.

EDIT: I remember comparing a bag of sample Madbull BB's (.2's) against some other .25's (I think MT or Bastards) for accuracy testing. I remember thinking "wow these madbulls sure got some extra range on them!"...then I remember they were only .2's.

Last edited by Flatlander; December 21st, 2007 at 23:27..
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