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Ok Im going to touch on several topics here to help maybe clear things up here... and yes it is going to be lengthy and include a lot of math and physics. Just skip the parts you don't want to read.

Back in early 2003 a guy going by cybersloth started posting theoretical Fluid Dynamics testing within AirSoft tolerances. This got me thinking.. and I started using his test data to actually field test my set ups.. the results were quite surprising as my set ups fell within +/- 5 ft of his results. Now 10ft. variance may not be the most accurate but it was certainly a good starting point from tabular data. By 2005 cybersloth had published what I would call the ultimate airsoft tome.. The AirSoft Trajectory Project.
You can find it here >>>

It is why when I get asked to help people make their Rifles more accurate, or shoot farther, or all of the above. I usually start with the Projectile (BB). There are other factors that come into play but lets cover those as we need to. Back in the early days when this sport was being developed in Asia. Many many tests were conducted to determine the best amo versus reliable amo... materials for barrels, lengths for barrels, propulsion systems (Spring vs. Gas vs. Electric) ect..ect.. I'm sure you get the gist.

What I took from these early tests found was that there was a certain relationship between the
(a) BB diameter ..TO.. (b) the inner barrel Diameter
(c) the inner barrel volume ..TO.. (d) the Cylinder volume.

It is these 4 components I balance in my systems... For the desired "Effective Ranges" I want out of a Weapon System. This is not to say that Hop-Up or Air Seals don't also come into play. They do and they are incredibly important. But people ask all the time whats better a 6.01 PDI or a stock brass 6.08. AND the answer is.. It Depends on how these 4 components work or don't work together.

There is a lot of talk all over the internet about what BB or Barrel is the best and I have tried a lot of them. I personally like Prometheus the best but I have also gotten great results with a MadBull.. and over the years I have tried and collected a lot of parts. Now I have several sets of barrels for all of my weapons in various lengths.. I can trade them out like golf clubs for different kinds of shots.

Now my point to all that is the Asia test studies showed a BB to Barrel variance should be about ~.08mm

<<<<< BB Data found on the net that have proven to be reliable >>>>>

<<<<< BB .2g >>>>>
Matrix .2g tracer: - AVG = 5.919 - Std. Dev. = 0.0199
smooth; sinks at the injection gate visible; not consistent spherically; very hard;

Matrix .2g whites: - AVG = 5.932 - Std. Dev. = 0.0187
very hard; very inconsistent roundness....saw variance on individual BBs of up to 0.1mm (example: 5.88-5.98mm); shiny; slight surface texture; found a sprue in the bag; one BB had very noticeable sink mark

Javelin 0.2g match grade bio: - AVG = 5.932mm - Std. Dev. = 0.009
Speckled surface, some very light roughness, gate marks visible; on the larger side of diameter; very good diameter consistency from BB to BB but roundness was poor. Pretty soft when crushed with pliers.

KillerBeez .2g whites: - AVG = 5.939 - Std. Dev. = 0.0137
Very shiny, smooth surface. Large average diameter, but roundness and consistency from BB to BB is fairly poor. One BB would be down at 5.91mm, while next would be 5.96mm. Very good hardness.

BB Bastard 0.2 STY: - AVG = 5.913mm - Std. Dev. = 0.1824
hard, just deform when crushed, shiny,

BB Bastard 0.2 ECO: - AVG = 5.948mm - Std. Dev. = 0.005

smooth, shiny, brittle, fragment when crushed

<<<<< BB .23g >>>>>
AE .23g: - AVG = 5.931mm - Std. Dev. = 0.0136
Smooth and shiny; good average diameter, but varied in roundness; several would measure consistently but then a rogue BB would be mixed in; good hardness

<<<<< BB .25g >>>>>
AE .25: - AVG = 5.95 - Std. Dev. = 0.0086
Smooth and shiny; very consistent spherically; very hard

Evike .25: - AVG = 5.909mm - Std. Dev. = 0.0194

Smooth and shiny; injection gate was visible; not spherically consistent at all; fairly hard

KSC .25: - AVG = 5.908 - Std. Dev. = 0.0085
Smooth and shiny; consistent spherically; good hardness

Straight .25 tracer: - AVG = 5.906mm - Std. Dev. = 0.0106

Smooth and shiny; injection gate was visible; seam lines perceptible; not spherically consistent at all

ICS .25g: - AVG = 5.935mm - Std. Dev. = 0.0121
Surface roughness apparent, but fairly smooth; good average diameter, but they were middle-of-the-pack at best for consistency; good hardness

KillerBeez .25g eco-friendly (tan): - AVG = 5.916 - Std. Dev. = .0063
Smooth, shiny surface; average diameter listed is a bit small because roundness is sketchy but the BBs physically measure on large side which has them chrono on the high side; great hardness

KillerBeez .25g whites: - AVG = 5.929 - Std. Dev. = 0.0085
Shiny, smooth surface. Pretty good average diameter, but roundness was not good; also variation between BBs was large, as one BB would be 5.94mm while the next would be 5.91mm. Very good hardness.

Echo1 0.25g match grade: - AVG = 5.928mm - Std. Dev. = 0.0062
Smooth, shiny surface; average diameter; great diameter consistency from BB to BB and roundness was pretty good. Pretty soft when crushed with pliers.

BB Bastard 0.25 STY: - AVG = 5.941mm - Std. Dev. = 0.005
hard, just deform, shiny, smooth

BB Bastard 0.25 ECO: - AVG = 5.95mm - Std. Dev. = 0.003
smooth, hard, shiny, brittle, fragment when crushed

<<<<< BB .28g >>>>>
Infinity .28: - AVG = 5.905 - Std. Dev. = 0.0114
Smooth and shiny; not consistent spherically; good hardness

G&P .28: - AVG = 5.935 - Std. Dev. = 0.019
Smooth and shiny; not consistent spherically; some noticeable rogue BBs; good hardness

Toyjet .28: - AVG = 5.895 - Std. Dev. = 0.008
Smooth and shiny; fairly consistent spherically; good hardness

Guarder .28: - AVG = 5.904 - Std. Dev. = 0.0086
Very shiny and slight surface roughness; average roundness; seemed slightly softer than other brands; good consistency

AE .28: - AVG = 5.962 - Std. Dev. = 0.0106
shiny; smooth; good hardness; good roundness; very large in diameter average

KillerBeez .28g whites: - AVG = 5.92 - Std. Dev. = 0.0159
Smooth, shiny surface; Middle of the pack average diameter, but consistency from BB to BB is terrible. Roundness was ok. Very good hardness.

G&G .28g bio: - AVG = 5.909mm - Std. Dev. = 0.0054
Fairly smooth, some very light roughness; a bit on the small side for diameter; excellent diameter consistency from BB to BB. Roundness was excellent also. Very brittle as they crack and fragment easily with pliers, but decent hardness.

PHX .28g: - AVG = 5.952mm - Std. Dev. = 0.0063
Slight surface roughness detected and shiny; great average diameter and very consistent in size, but they showed some variance in roundness; they were easy to crush compared to others

BB Bastard 0.28 STY: - AVG = 5.941mm - Std. Dev. = 0.006
hard, just deforms, roundness is suspect, shiny, smooth

BB Bastard 0.28 ECO: - AVG = 5.929mm - Std. Dev. = 0.003
decent roundness, hard, shiny, smooth, brittle

BB Bastard 0.28 SIL: - AVG = 5.954mm - Std. Dev. = 0.005
these are glass-style BBs. VERY brittle and they do indeed shatter, good roundness, smooth, very hard

<<<<< BB .29g >>>>>
Maruzen Super GrandMaster .29: - AVG = 5.931 - Std. Dev. = 0.005
Smooth and semi-shiny; exceptional spherical roundness; very consistent size

<<<<< BB .30g >>>>>
Maruzen .3: - AVG = 5.904 - Std. Dev. = 0.0218
Semi-shiny; semi-smooth; can see speckles; somewhat soft

Straight .3 silvers: - AVG = 5.904 - Std. Dev. = 0.015
Smooth and shiny; fairly consistent spherically

Toyjet .3: - AVG = 5.873 - Std. Dev. = 0.009
Smooth and shiny; speckled; average roundness; a couple rogue smaller BBs; good hardness

Tokyo Marui .3g Precision: - AVG = 5.937mm - Std. Dev. = 0.0048

Smooth and shiny; no seamlines, injection marks; very consistent roundness; excellent hardness

BB Bastard 0.3 STY: - AVG = 5.943mm - Std. Dev. = 0.009
below average roundness, injection dimples, smooth, shiny, deform

<<<<< BB .36g >>>>>
BB Bastard 0.36g Nites: - AVG = 5.950mm - Std. Dev. = 0.0012
excellent roundness, smooth, very shiny/glossy, extremely hard, could not break them

MadBull 0.40g Tan: - AVG = 5.913mm - Std. Dev. = 0.004
Smooth and shiny; average roundness; good hardness

<<<<< BB .40g >>>>>
MadBull 0.40g Tan: - AVG = 5.903mm - Std. Dev. = 0.003
Smooth and shiny; average roundness; good hardness

<<<<< BB .66g >>>>>
BB Bastard 0.66g Pearls: - AVG = 5.949mm - Std. Dev. = 0.001 ($11.95 for 8 BBs)
excellent roundness, smooth, very shiny/glossy, extremely hard, could not break them


For starters, simple physics dictates that as an object increases in speed, air resistance (drag) also increases.
Second, in order to have optimal performance / efficiency, it is important for the projectile (BB) to reach terminal velocity as it leaves the barrel.
To accomplish that, the pressure pulses propelling the BB cannot become lower than that of air resistance during any time within the barrel.
From those facts, we can derive that the cylinder volume will always have to be greater than barrel volume.

As to the actual "optimal" cylinder to barrel volume ratio, it depends on each system in question.
The ratio increases as Stiffer Springs are used for obvious reasons mentioned earlier.
From various experiments for stock AEGs with barrels shorter than 500mm, the ratio is about 1.5 to 1 ... for barrels 500mm and above it raises to 2 to 1.

<<<<< Formula to Determine Cylinder Volume >>>>> ( Pi x Radius[Squared] x Height )


Here is the write up on the Barrel Suck Myth... Skip it if you know it or don't want to read it. (Appiles to anyone using an AEG DMR)

There is a concept in AirSoft called "Barrel Suck." It is the idea or phenomenon that apparently occurs when an AEG piston begins retracting while a BB is still in the barrel, causing a loss in BB velocity due to the piston sucking back air from the barrel behind the BB. I have searched the web and here is what I believe is the evidence to prove it's a myth and doesn't really exist in practical AirSoft. (I would give credit to the guy who wrote the original info but I can't find any details or the original site. Just know there are some smart AirSofters out there trying to make this a better sport.)


FPS: Feet per Second - Velocity of the airsoft projectile
IPS: Inches per Second (FPS X 12) used for calculations.
ROF: Cyclic rate of fire measured in Rounds per Second.
Conversions: mm X 0.03937 = Length in Inches

So lets start with a fictional worst case scenario. LONG BARREL with a LOW FPS and a HIGH ROF

Long Inner Barrel = 600mm (Conversion = 600 X 0.03937 = 23.62" let's call it 24")
Low FPS = 250
High ROF = 20 rps

At 250 FPS, it takes a BB 0.008 seconds to travel 24" (1sec / 250fps = .004 X 2ft)

At 20rps, a BB is fired once every .05 seconds. (1sec / 20rps) and since the sector gear turns at a pretty consistent rate it can easily be assumed that it would take half that time to re engage the gear teeth or .025 seconds

Assuming Zero Point on our timeline to be the point where the piston releases from the sector gear, the BB exits the barrel at approximately 0.008 seconds, leaving 0.042 seconds before the next shot even begins to travel down the barrel... but more importantly... leaving 0.017 seconds before the Piston Starts to get pulled back creating the sucking action. (0.025sec -minus- 0.008sec)

What this means is the BB will be 4.25 ft outside and away from the barrel before the "Suck" Occurs.
What this also means is your Weapon System Barrel would need to be 1980 mm or 6.5 ft for this to possibly be a reality.

Now if you really want to you can figure out your own weapon system using the Math provided but in reality I wouldn't loose any sleep over this.

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Wow my head hurts, lol that's a lot of info but very nice this should be pinned for future proposes. I really like the BB section on here, on this post that is.

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107 Posts
Nice work, Mojo. Also I have heard that the "barrel suck" means the wrong ration with cylinder/barrel volume, like you talked about in the "CYLINDER VOLUME" part. Just a tought.

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Discussion Starter · #8 ·
Never used BBKing .32g... hell I always thought he was a blues artist never knew he made BBs too.

but if you come across a good review on BBs I will update the post to include the new info..
but please make sure its reliable.

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164 Posts
Very nice a lot of useful info for beginner up to experienced players keep the info flowing if you can this is great stuff

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89 Posts
what upgrades do you guys recommend for a 500 FPS DE Metal Bolt Action L96 AWP Airsoft Spring Sniper Rifle MK96 and it has a 3-9x32 Zoom Scope already. any upgrades? i dont really need to upgrade the spring so you can exclude that.
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