http://www.filairsoft.com/forum/showthread.php?t=41470

Some of the pistures are missing. Use the link above to get the whole deal.


Tech Info

This Page was taken from a post of Skipperooo in FAS Tech Forum.
Welcome to FAS [Tech n' Maint Forum] Posted here are collection of technical information from previous forum threads (FAS/AGL) and general facts from experienced veteran gunsmiths and players: Thank you!

DISASSEMBLY: Step by step guide on disassembling TM Gearboxes at airsoftguns.com
Click Here for TM Version 2 Gearbox Disassembly Guide
Click Here for TM Version 3 Gearbox Disassembly Guide

Click Here for TM M16 Series Gun Disassembly Pic Guide

**parts graphic reference at http://filairsoft.com/airsoft106.htm

SPRINGS: (Approx. Settled Spring FPS on .20gBB)
Stock Gun (brand new gun) = 270-290 FPS
CQB Gun: M100 / SP100 / PDI120% = 330-350 FPS << FAP CQB Standard
Standard Field Gun: M120 / SP120 / PDI170% = 390-410 FPS [.20gBB stable] << COMMON UPGRADE
Std High Field Gun 1: M130 / SP130 / PDI190% / PDI210% = 440-460 FPS [.20gBBmin .23gBB stable]
Std High Field Gun 2: M140 / SP140 / PDI240% = 470-490 FPS [.23gBBmin .25gBB stable]
Sniper Field Gun 1: M150 / SP150 / PDI270% = 510-530FPS [.28gBB stable] << FAP Sniper Standard
Sniper Field Gun 2: M160 / SP160 = 550-580FPS [.30g/.36gBB sweet-stable] << rat buster
Sniper Field Gun 3: M170 / SP170 = 580-600+ FPS [.36g/.43gBB sweet-stable] << cat buster
Spring Power Chart http://filairsoft.com/airsoft103.htm
BB goes wild = BB too light -- BB range seems near = BB too heavy

GEARS: (Does NOT affect Gun FPS, only ROF)
Infinite=(1) Ultra=(2) SuperTorqueUp=(3) TorqueUp=(4) StockRatio=(5) FastGear=(6)
>> Numbers indicate "car-gear-shift". *Small batts (non Sub-C) DOWNSHIFT to next LOWER gear. <<
Common Gear-to-Spring Setup for Big Batt (engine) (Sub-C):
Fast Gears (6) - UP TO M100 / SP100 / PDI120%
Stock Gears (5) can 'safely' handle up to M130, SP130, PDI190% <<<< on 9.6v 1700mAh(min)
Torque Up Gears (4) - M130 / SP130 / PDI190%-210% or LOWER
Torque Up Gears OR Super Torque Up (4/3) - M140 / SP140 / PDI240%
Ultra Torque Up Gears (2) - M150 / SP150 / PDI270%
Ultra or Infinite Gears (2/1) - M160 / SP160 << Needs minor machining to fit on Ver.2 GearBox
Infinite Torque Up Gears (1) - M170 / SP170 << Needs minor machining to fit on Ver.2 GearBox
*Some Gear set won't fit on some reinforced Gearbox-CHECK first before you get one.
*No known machining on stock ver.3 GearBox to fit any gear set.
*AVOID using Bearing Bushings on M120 above. only for soft springs

M130 / SP130 / PDI190%-PDI210% on STOCK Gears will last Approx. 5-10 months (depends on use)
Stock Gears - Low Cost, nice ROF. will not last long. (cast alloy)
Flat Gears - Noisier, Cheaper. More durable (steel)
Helical Gears - Silent. Expensive. shimming sensitive (steel) <<Avoid pairing w/ Bearing Bushings

BATTERY: (Does NOT affect Gun FPS, only ROF and Rounds of fire)
Voltage = Rate of Fire (ROF) mAh = BB-Rounds (Power/Stamina)
BIG INTERNAL Standard Battery Size [Ni-CAD]:
M4A1 - 9.6v 1700mAh (Fat-long AA) V-Type 12v 1700mAh(max)
M4A1 Patriot - 12v 1700mah (Fat-long AA) Circular config
G36C - 9.6v 1500mAh (Fat AA)
M733 - 9.6v 1500mAh (Fat AA) Chako-Type 12v 1700mAh(max)
AK 47/Spetz - 10.4 2400mAh (Sub-C) 12v(max)
M16A1/A2/VN/SR16 - 9.6v 2400mAh (Sub-C) 13.2v(max)
CAR15 - 8.4v 600mAh (Small) 1500mAh (max) (Fat AA) 2-separates
P90 - 9.6v 1700mAh (Fat-long AA) J-Type
G3A3,G3SG1,MP5A4,MP5SD5 - 9.6v 2400mAh (Sub-C) Straight
MP5SD6 - 9.6v 1500mAh (Fat AA) V-type
MP5A5 - 9.6v 1100mAh (Slim) Chako-Type << (?)
Steyr AUG - 9.6v 1700mAh (Fat-long AA) Box-Type
PSG-1 10.8v 1500mAh (Fat AA) 13.2v(max)
M16 Dummy/Ready MAG - 9pcs 10.8v 1700mAh (Fat-long AA)
AN/PEQ 2 Dummy Laser Box - 9.6v 1700mAh (w/laser) 12v 1700mAh(max)

Approx. Battery-to-Rounds Capacity: [NiCd] (on M120 Stock Gears, EG1000)
9.6v 600mAh = <500 rounds (Small) Sanyo KR600AE 9.5mOhm Internal Resistance
9.6v 1100mAh = 1,000 rounds (Slim) Sanyo KR1100AAU 19mOhm Internal Resistance
9.6v 1500mAh = 1,400 rounds (Fat AA) Sanyo KR1500AUL 16mOhm Internal Resistance
9.6v 1700mAh = 1,800 rounds (Fat-long AA) Sanyo KR1700AU 17mOhm Int. Resistance
9.6v 1900mAh = 2,400 rounds (Sub-C) Sanyo N-1900SCR 4mOhm Internal Resistance
9.6v 2000mAh = 2,600 rounds (Sub-C) Sanyo KR-CH 6.5mOhm Internal Resistance
9.6v 2400mAh = 3,100 rounds (Sub-C) Sanyo CP-2400SCR 4.5mOhm Internal Resistance
9.6v 3000mAh = 3,800 rounds (Sub-C) Sanyo HR-SCU [Ni-MH] 5.3mOhm Internal Resistance
*can someone confirm this rounds guesstimation--
BEST BUY: 9.6v 1700mAh(small-type) 9.6v 2400mAh(large-type)

Approx. CHARGING Time on 1000mAh Output Charger:
600mAh = 36mins(min) 42mins(std) 48mins(max)
1100mAh = 1hr 6mins(min) 1hr 19mins(std) 1hr 30mins(max)
1500mAh = 1hr 20mins(min) 1hr 48mins(std) 2hrs 7mins(max)
1700mAh = 1hr 42mins(min) 2hrs(standard) 2hrs 24mins(max)
1900mAh = 1hr 53mins(min) 2hrs 18mins(std) 2hrs 43mins(max)
2000mAh = 2hours(minimum) 2hrs 24mins(std) 2hrs 48mins(max)
2400mAh = 2hrs 23mins(min) 2hrs 54mins(std) 3hrs24mins(max)
3000mAh = 3hours(min) 3hrs 37mins(std) 4hrs 13mins(max)
*Charger should be 1 to 3 volts higher voltage than total battery voltage
Go over to http://digibattery.com for more battery-charging-time calculations
DISCHARGING: Number of batteries in a Pack = Max discharge volts.
(ex. 9.6v = 8cells in a pack = 8.0v is the maximum discharged voltage)

PISTON: Depends on your spring and trigger abuse.
M140 Above = Aluminum Piston (for ratatat players)
. Choice1: ICS Aluminum Piston
. Choice2: Systema Aluminum Piston
*if compatible, get the half-tooth to lessen the weight
M140 Below = Polycarbonate Piston
. Choice1: Guarder Polycarb Piston (blue)
. Choice2: Tokyo Marui Stock Piston (white) <-- polycarbonate too
. Choice3: Systema Polycarb Piston (black) << brittle bad choice
AVOID the RED PISTON-Systema Polycarb (defective) there's a newer version
*have'nt tried the TGS(blue) nor the TOP yet, but it looks promising <-- pls review
*some use polycarbs on m140 above but with trigger care

CYLINDER: (cylinderVolume-to-barrel-ratio) 2 is to 1 (standard)
Marui Stock Cylinders:
1. Closed Cylinder = 27.1cc 450mm(min) 580mm(max) barrel length
2. XM Cylinder = "4/5 hole" = 364mm(min) 460mm(max) barrel length
3. M4 Cylinder = "3/4 hole" aka Type-2 17cc - 229mm(min) 430mm(max) barrel length
4. MP5K Cylinder = "mid hole" 9cc 110mm(min) 170mm(max) barrel length

Systema NB Standard and BoreUp Parts:
1. Type-0 Cylinder (closed) fits M16-A1,VN,A2,G3-A4,SG1,SIG550,AUG
2. Type-1 Cylinder (tip hole) for XM177, M4, AK47, AK47S, SIG551
3. Type-2 Cylinder (XM hole) for MP5-A4,A5,SD5,SD6, MC51,SIG552
4. Type-3 Cylinder (M4 "3/4" hole) for MP5 PDW
5. Type-4 Cylinder (MP5K mid hole) for MP5K
*BoreUp Closed 29.4cc = 500mm(min) 600mm(max) barrel length


KM Cylinder Parts:
*Intercept Cylinder 59 barrel length from 450mm to 590mm (Type 0)
*Intercept Cylinder 45 barrel length from 250mm to 450mm (Type 2)
*Intercept Cylinder 25 barrel length from 100mm to 250mm (Mid-hole)

*To avoid confusion, don't mix brand model names, just model equivalence
*TM M733 by stock is closed cylinder (Type 0) -over ratio

RATIO Guide: Standard-Efficient Ratio is 1.5 is to 1
2-2.5 : 1 for springs up to M130 --- 2.5-3.0 : 1 for strong springs M140 -> UP
<needs further research>

BARREL: (inner barrel length)
650mm/25.59in PSG-1 (extended)
595mm/23.42in APS2 OR
589mm/23.18in PSG-1
550mm/21.65in M16A1/VN/A2,AUG (extended)
534mm/21.02in Sig550
509mm/20.03in M16A1/VN/A2,AUG
472mm/18.58in Famas SV/F1
469mm/18.46in G3-A3/A4,SG1
455mm/17.91in AK47,AK47s
444mm/17.48in M60
407mm/16.02in M4A1 M653E2 (extended)
395mm/15.55in APS2 SV
369mm/14.52in HK51
363mm/14.29in M4A1,RIS,SR-16,XM177ED,Sig551
300mm/11.81in M1A1,AKBetaSpetz, M733
285mm/11.22in MC51
247mm/9.72in Car15,P90,G36C, SIG552
245mm/9.64in UZI - 400mm/15.74in (extended)
229mm/9.01in MP5A5/A4/SD5/SD6
170mm/6.69in MP5K-PDW (extended)
141mm/5.55in MP5K-PDW
110mm/4.33in MP5K

MOTORS:
TM EG560 (famas)
TM EG700 (need more spec info)
TM EG1000 27,552rpm 1,407.00G.cm Torque
Systema "Genuine" 29,825rpm 1,6999.83G.cm Torque
Systema "Hi-Speed" 37,400rpm 1,915.99G.cm Torque
Systema "Hi-Torque" 32,302rpm 1,932.49G.cm Torque
Systema "Super Hi-Torque" 34,787rpm 1,998.47G.cm Torque
Eagle Force Hummer 1100 (high-speed)
Eagle Force Hummer 1300 (super-high-speed)

GAS: (for gas guns/pistols)
Freon12/Flon12 (94psi) = HFC134a (97psi) a.k.a. Green Gas
Freon22/Flon22 (140psi) a.k.a. TOP Gas, Taiwanese Green Gas,Omega Gas,ToyJack Gas
RED Gas = a bit higher pressure (?) than TOP Gas
BLACK Gas = highest pressure for airsoft <carbon<myth?
*pressures on 30C / 86F manila temp. / gas expansion speed differs from each type of gas
__________________
SHIMMING GUIDE: taken from wajoegween
AEG: Shimming
1) Preparation - Remove everything from the mechbox that will get in the way of getting to the gears. This includes the spring/piston/cylinder assembly, and then it depends on the gear box. With version two mechboxes, the little safety lever needs to be removed so that the selector plate can be slide forward and off. Now there should be only the trigger assembly left in place. With other versions, other parts may or may not need to be removed. When checking shimming, do not install the anti-reversal latch, motor or anything else that may restrict the gears movements in either forwards or backwards.
2) Shims and Bushings
[note: I speak only of Systema shims. I am not familiar with stock or other shims. For simplicity, I always replace all shims with Systema ones.]
There are three different sizes of shims, 0.5mm, 0.3mm, and 0.2mm thickness. There are two different diameters of shims, the small and the large. Of the two smaller diameter shims, they are noticeably different in thickness. They are the .2mm and .5mm thick shims. The large diameter shims are the .3mm thick ones. Since your reading this guide, your are most likely replacing the bushings. If the replacements are solid metal they will be a tight fit. I first try pressuring them into place by pushing with my thumb really hard. If it does not pop into place, I take something soft and tap it into place. Most commonly I end up lightly hammering them in using the plastic handle of a screw driver. Make sure to force the bushings into place EVENLY! If you are replacing the stock bushings with bearing bushings, they will be a loose fit, and it is easier to put them on the gears than to try to make them stay in place on the mechbox. Don't worry about how unstable the bearings feel, they will be plenty beefy when the mechbox is together.
3) Spur Gear
On the bottom(left) side of the gear, place a single .3mm shim. With the Fa-Mas, it might be necessary to have more shims than any other mechbox. With my only Fa-Mas shimming experience, I had to use two .3mm shims on that side, and generally a lot of shims all around. Put the gear into its place, and put the top(right) half of the mechbox on, and just hold them together tightly with your hands. Push the axle with a tooth pick or something similar, and note about how much it moves. Now it's just a game of guess and check with shims on the top(right) part of the spur gear. Once you think you have it just right, with little to no movement, put in three or four screws to make sure its held tightly(more than your hand can do). It should have very little or no movement side to side, AND you should be able to reach a finger in through the empty cylinder hole and freely spin the gear. If there is too many shims on the upper axle part, it will have resistance or be completely stuck. If there are too few shims, it will turn freely but have too much side to side movement.
4) Bevel Gear
Start with the bottom(left) half of the mechbox including the shimmed spur gear. Place two .2mm shims on the bottom(left) part of the axle and put it in its place in the bottom(left) half of the mechbox. Check for clearance between the teeth of the spur gear that mesh with the normal teeth of the bevel gear and the notched part that the anti reversal latch rides on.* If they interfere with each other, then the bevel gear needs more shims on the bottom(left). If there is ample clearance (unlikely), you may want to drop it down to a single .3mm shim. The idea here is: You do not want to compromise the gears' teeth because of the bevel gear having too many bottom(left) shims leading to minimal gear tooth surface contact between gears, but at the same time you don't want the anti-reversal latch contact area to be grinding with the spur gear. OK, enough rambling. Throw the right side on and check for movement the same way you did for the spur gear. Then guess and check, put in a few screws and do the final spin check with the two gears. Re-adjust and re-test as needed.
5) Sector Gear
Almost exactly like the bevel gear, start with the bottom(left) half of the mechbox including the shimmed spur gear and bevel gear. Place one .2mm shim and one .5mm shim on the bottom(left) part of the axle. Check for clearance.* This time you want to make sure the large diameter part of the spur gear is not going to be binding with the teeth on the sector gear that engage the spur gear on it's smaller diameter part.
*A general note about gear clearance: Remember that when the mechbox is together, the gears will not be able to twist(axels slightly off of parallel) relative to each other, so when checking the clearance, you may see interference that should not be there since you only have one half of the mechbox on. Make sure to not accidentally over shim the bottom(right) side of the bevel or sector gears because of this.
HOLY CRAP LOOK AT ALL THE INFO - JUST TO KILL A TANGO
*thank you to all those who contributed to the list! if you want to add to the reference, just reply to this thread

- Filipino Airsoft Technical Forum -
- Tech Reference revision 8.1 -

Upgrades:
After a while most players begin to think about upgrades and to improve their weapon. The first thought is probably to increase the muzzle velocity to gain extra range. But the only weapon that needs longer ranges is rifles like sniper rifles and the real important upgrades isn't to improve performance but to make the weapon more durable and to increase lifespan. Most players settle for only changing the battery to a bigger and to put in a slightly stronger spring. When an Airsoft weapon is upgraded to increase muzzle velocity the weapons lifespan will decrease. How powerful an Airsoft weapon is depends on three things. The strength of the spring that pushes the piston forward, the amount of air the piston compress and the precision of the barrel. When a weapon is highly upgraded it becomes a specialized tool for serious Airsoft skirmish and to dry-fire (i.e. without bullets) puts even more strain on the parts.

Spring:
There is two ways to measure how strong a spring is compared to a standard spring. There's the Percentage system and the Meter Per Second system. A standard AEG has a muzzle velocity of 90m/s (100%) with a 0.20g bullet. A M100 spring increases this velocity to 100m/s. The corresponding spring in the percentage system is 110%. There are M100, M110, M120, M130, M140, M150 and M160 springs. A very powerful spring requires that the entire gearbox be replaced.

Bearings & bushings:
The axles inside the gearbox is attached to the housing by small plastic bearings and these will eventually wear down. If these bearings are exchanged to metal or ball bearings, the lifespan of the mechbox will increase (almost double according to many players). Bushings are small thin plates that make sure that the gears in the gearbox are precisely aligned. These can be changed to "Accelerated" synthetic ones to reduce wear, although I personally trust the metal ones more than the accelerated.

Barrel:
The barrel in a standard Airsoft often has a internal diameter of 6.12mm. If this barrel is exchanged for a precision barrel with a 6.04 mm internal diameter the amount of air that slips by the bullet reduces and the benefits is that the bullet has less spread and about 5% extra velocity. The downside is that the barrel clogs up more often and has to be cleaned. A longer barrel increase range, but the barrel can't be too long since if the amount of air in the barrel is more than the amount of air the piston push forward, a vacuum will develop in the barrel and the bullet will be sucked back with a big speed reducement. There is a method called "Crater-cutting" that has the effect that just before the bullet leaves the barrel the air slips by and cuts a hole in the wall of air that is formed in front of the barrel. This isn't something for the common player and this is only used by the players that try to increase the range as much as possible.

Battery:
If a batteries voltage increase, so do the rounds per minute in an AEG motor. All standard AEG batteries has a voltage of 8.4Volts and the only difference between the different sizes is that a Large battery has a capacity of 1300mAh, while the other small standard batteries has capacity of 600mAh. This means that a large battery will last for about twice the amount of shots. Upgrades inside a gearbox often reduce the rate of fire and if you then use a battery with a higher voltage like 9.6V or 10.8V the rate of fire wont drop as much or even increase. A higher voltage also wears a motor down faster and more maintenance is required. It is possible to use 12V to power an AEG but this isn't to recommend since the wear is increase very much, the contacts in the trigger is faster worn out and the overall lifespan is sharply reduced. A battery with a higher capacity (more mAh), can be used under a longer time and can fire more shots. Upgraded weapons also require more current and the amount of shots that can be fired will decrease unless a bigger battery is used. The usual batteries are NiCd (Nickel Cadmium), but there is another type called NiMH (Nickel Metal Hybrid). The NiMH usually has a higher capacity (mAh), but they can't handle big currents very well and so they don't work well to most Airsoft weapons unless they're very big (about 3000-5000mAh). NiMH is more expensive and harder to charge and they shouldn't be fast charged.

When do you need to get a better battery? All AEG's either use the 8.4V 600 mah (Mini) or the 1300 mah (Large) in stock configurations. If you chose to upgrade an AEG's with a more powerful spring and gear set. The original batteries will not be sufficient for extended play. Your battery will drain faster due to the increased resistance of the heavier spring. For better performance and rate of fire, a 8.4V 2000 mah ( large type ) or 9.6V battery is highly recommended. For the AEG's that can only accommodate the mini type battery. The only option after gear box modifications is installing a 9.6V mini type battery for increased endurance or one can use an external battery. In some cases the 9.6V batteries may require slight modifications to your AEG in order to fit in the allotted battery space. We also have some special types of batteries for various types of AEG's these batteries come in special configurations that take into effect the space available inside your AEG. Some may also require modifications to your AEG, to fit correctly.

Gears:
The normal gears in a gearbox has an approximate lifespan of 30'000 shots, a new set of gears will last longer since they're made from better material. There is a set that increase rate of fire and reduce the motors power or reduce rate of fire but increase the motors power. The "Helical Cut Gears" is special gears that has a better grip between the gears and doesn't brake as easy as standard gears. The biggest supplier of upgrade and replacement parts i Systema.

Nozzle:
This is a small metal or plastic nozzle that transfers the air from the cylinder to the bullet. This is a cheap upgrade and the muzzle velocity increases slightly.

Motor:
Most upgrades reduce the rate of fire. By switching to a stronger motor the rate of fire isn't reduced as much. An upgraded AEG should have at least an EG700 motor. The strongest motor is EG1000. All new models that Tokyo Marui releases have EG1000 motors, but many of the older models have EG700 or even EG560. Not all AEG can have a motor upgrade. If the spring isn't replaced with a stronger than M120 the EG560 motor can take it, but the battery will probably has to be changed to a 9,6V or even 10.8V.

Piston:
A piston can be equipped with a "Silent" or "Anti-Vacuum" piston head. The silent piston head reduce the impact the piston makes in the cylinder and also reduce noise. The Anti Vacuum piston head prevents the forming of vacuum in the cylinder.

Mechbox:
This is a totally new mechbox with new and better gears, stronger spring, nozzle and other improvements. This isn't a cheap upgrade but the durability and lifespan increase and so do the muzzle velocity and overall performance. A new mechbox isn't available to all models, like the FAMAS doesn't have a upgraded mechbox. There are different versions of mechboxes since they're used in different weapon models. Version 1 is only used in FA MAS. Version 2 is the most common and is used in M16, G3 and the MP5s. Version 3 is used in AK47, MP5K & MP5K PDW and Sig SG55x. Version 4 is only used in the PSG-1 and is only semi automatic. Version 5 is used in the UZI and has the recoil system.

Airsoft for Rookies - The Beginners guide
By: Ronny "Thinker" Ohlsson


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1)Piston Head O-ring
Common cause: Worn out or sometimes even new ones shrunk in time or incorrect size (Bore up or non bore up)
Suggestion: Replace

2) Cylinder Head O-ring
Common cause: Worn out, sometimes shrunk in time or incorrect size (Bore up or non bore up)
Suggestion: Change Oring or wrap a few layers of teflon tape until its tight enough with the cylinder, Or replace with double o-ring type Cylinder head

3)Nozzle
Common cause - Worn out nozzle or incorrect nozzle size. I think nozzle size varies with the type of gun so its not a one size fits all. In adddition there are Bore up and non bore up type of nozzle.
Note: Nozzle slides with the Cylinder head nozzle, you cant make it too tight otherwise nozzle woulndt slide at all so they are bound to have leaks, but the key is to minimize it.
Suggestion: Replace with an air sealed nozzle or the one with O-ring type (havent seen one though).

4)Mating of Hop rubber and nozzle
Common cause: Worn Hop rubber (lips torn) and/or worn nozzle tip, incorrect nozzle length or size
Suggstion: Replace

5)Fit between Hop rubber and Inner barrel
Common cause: At certain pressure the hop up rubber tends to balloon out from the air pressure thats chaneling from the small opening of the inner barrel (where the small hop rubber goes in).
Suggestion: To prevent this, after inserting the inner barrel to the hop up rubber wrap a few layer of teflon outside the hop rubber so it will hug the inner barrel more but thin enough so it will still go in to the hop up chamber.


piston porting:


taken from FAS. (almighty)


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taken from XTR's post in one of the older versions of FAS.


shimming instructions:
http://rapidshare.com/files/12429068...ON_to_shim.doc

MOTOR science:

The graph above shows a torque/speed curve of a typical D.C. motor. Note that torque is inversely proportioal to the speed of the output shaft. In other words, there is a tradeoff between how much torque a motor delivers, and how fast the output shaft spins. Motor characteristics are frequently given as two points on this graph:
• The stall torque, , represents the point on the graph at which the torque is a maximum, but the shaft is not rotating.
• The no load speed, , is the maximum output speed of the motor (when no torque is applied to the output shaft).

__________________

got this from another forum, hope it helps explain some points in our hobby

Cylinder volume - if the cylinder does not have the internal volume to hold enough air to propel a BB down a certain barrel length, the BB will slow down in the barrel due to not longer being accelerated by a force behind it (air pressure). Conversely, if it has more internal volume than the inner barrel, the BB will not reach full velocity before exiting the barrel because the initial rush of air is what propels the BB, not the full volume being expelled from the cylinder by the piston racing forward. An example would be Obsidian’s G3SAS: It has a very short inner barrel with a type0 cylinder if I recall correctly, so the BB is not reaching the full acceleration before exiting the barrel, so thus he installed a stronger spring to compensate. In other words, he is using a spring that is capable of more energy with parts that stunt that capability, thus allowing that particular gun to be legal. A different approach would be to use the appropriate cylinder for that short of a inner barrel length, which would allow that gun to reach about the same muzzle velocity with a weaker spring, thus saving some wear and tear on other mechbox internals. In those two scenarios, the gun has the same muzzle energy, but went two different routes to get there, with one being optimized for that barrel length and the other using brute force.

Thus, this is why various cylinder types (positioning of holes in the cylinder) are matched with certain barrel lengths, because you want as much air moving as fast as you can get it to be what is expelled through the nozzle.

When an AEG fires, it is expelling a set amount of air. Since the air from the cylinder is at the same pressure as the atmosphere, the BB is only accelerated by the volume of air behind it. This differs from a gas gun, in which a certain amount of gas is expelled or valve simply opened, which allows the propellant gas to expand rapidly and try to equalize with the atmosphere. In that case, the gas will actually cause the BB to gain velocity in the barrel as the gas increases speed in order to escape the barrel to equalize with the atmosphere.

Now in both cases, BB weight can cause various muzzle velocities without changing the spring. This is because a higher-powered gun is forcing air out that much faster. Thus, a light BB might be expelled very quickly by that initial burst and not reach the energy that the gun is actually capable of......in other words, if a heavier BB is used in that same gun, you can actually see a muzzle energy increase because the BB is heavy enough to not be shot forward by that initial burst. This means the full volume of air is behind it moving quickly, and it reaches full acceleration as it exits the barrel. A BB that reaches full acceleration earlier in the barrel will actually slow down as there is no force behind it anymore, so it is traveling on inertia alone and frictional forces, due to air and also the walls of the barrel, act to slow it down. This is relevant because with high-powered sniper rifles, testing is done with a .2g BB. This is faulty because the gun is tuned to shoot with a heavier BB, like .34g or greater, let's say. Thus, that lighter BB may exit the barrel before the full energy potential is reached. For instance, there have been cases where somebody will chrono at 490fps with a .2g BB which equates to 2.2J of energy. Then, they chrono with a .36g BB at 420fps which equates to 2.9J. Same gun, very different muzzle energy because of what I outlined above. That is where muzzle energy comes into play and is a better indicator of a gun's energy capability than pure velocity. You can see how that could come into play at the chrono pit, and a player innocently and unknowingly is wielding a gun that is shooting at higher muzzle energy than expected.

This is usually only seen in higher-powered guns, but can be seen in our regular AEGs as well to a smaller degree. For example, let's say you have a gun chrono at 400fps with .2g BB, which equates to 1.48J. I have seen multiple common instances where that same gun will then chrono at 360-370fps with .25g BB, which equates to 1.49-1.58J. See how the energy rise was slight, although the gun legally shot 400fps with .2g BB?

Thus, the relationship is not linear, but is dependant on parts in your gun, including the nozzle, tightbore barrel, piston head, cylinder, cylinder head and inner barrel length. Furthermore, if those parts aren’t sealing well, that throws a bit more variance into the mix. However, due to experiences with various guns, you can get a feel for where a gun should lie in the muzzle velocity range based on what BB is being used. So your statement about expecting a gun to shoot anywhere from 25-50fps higher with a .2g BB versus a .25g BB, as a loose general number, is accurate, although in my general experience I would typically say 30-40fps is a more likely number. I threw out 25-50fps earlier to incorporate more variables.

The same discussion mentioned above for sniper rifles and regular AEGs also applies to support weapons. For example, one of my RPKs chrono'd at 442-447fps consistently at the last Roanoke op with .2g BB, and prior to going to that op, I had checked it at home with .25g BB to be anywhere from 401-411fps. The .2g BB energy works out to 1.79-1.87J, whereas the .25g BB works out to 1.85-1.94J, so you see how the same gun can produce slight muzzle energy differences just because of the BB.

This ALSO is further complicated by the brand of BBs you use. Some brands are nominally smaller than other brands. For example, I have some KSC .25g BBs that a handful measured in the 5.92-5.96mm diameter range. Compare that to some AE .25g BBs that I measured that fell in at 5.94-5.97mm range. The AE had a smaller tolerance range and a slightly larger diameter, making them more consistent and accurate. This is more apparent in gas guns, in which the hopup systems differ than that of the AEGs, and I am still learning about that having picked up types of those guns in the past couple months.

Ok, I think the only thing I haven't covered is bore-up cylinders.......they have a slightly larger internal diameter for the purpose of being used with longer inner barrels with higher-powered springs. You would not use a bore-up in a short inner barrel gun for the reasons outlined earlier…..the BB would exit the barrel before full acceleration is achieved. I personally am not a big fan of them since they require a matching piston head, and those are not readily available to my knowledge, unless you buy the entire kit again. Therefore, I have less experience with these, but the same basics apply. The thought is that if you have a larger air volume in the cylinder as the source, along with a long inner barrel, that you can achieve greater muzzle velocity since you are allowing the BB to accelerate longer with a larger pressure behind it.

Basically overall, you would pick what inner barrel length you are seeking first, and then pick a cylinder type to match it.



Long barrels need Boreup Kits:
Since wolv didnt run over bore up cylinders.... bore up cylinders have a thinner cylinder wall as well as a larger bore on the cylinder head nozzle. Due to this larger bore the nozzle must be a larger bore. This basically gets you a minimal increase in volume throughout the whole system. It has the downside of each part being unique and non replaceable for the most part. Going to wolv's explanation I have seen several boreup kits that resulted in a drop of BB velocity. Not what someone wants after spending 50 to 100 bucks on an upgrade. This is due to their being a larger volume of air that the same sized spring is trying to push. So if your gun was shooting 400 with and you put in the boreup kit because you bought into the marketing hype you would probably end up shooting around 385 after. In my opinion they are a waste of money. To prove this I built a g36 up with a RAS and a 650 mm PSG barrel....longest barrel available on the market. I have an M120 and type 0 cylinder installed and the gun shoots consistantly 400 to 405.

You need a long barrel for range/fps/whatever. Barrels give you accuracy and can contribute to range due to the volume that they possess. I constantly hear about everyone wanting to make their barrel longer to get better range or more FPS. As you have seen it is a science. You need to have a barrel that matches the volume of air that your cylinder is pushing out. Your velocity is coming from the compression of the air from your spring. As wolv said if your barrel contains less volume than your cylinder you are wasting some of that compression your spring generates. My G3SAS has one of the shortest barrels out there. It actually has the stock cylinder in it which has a hole in it. With an M120 the gun will only shoot around 350fps. This is because the gun has half the barrel/cylinder volume of an SR16 for example. To compensate for this I put an M130 into the gun. This has the effect of compressing the air faster to generate more pressure. This gets the bb up to speed before it leaves the barrel. This results in it shooting 400 fps. Now lets look at the flip side....Longer barrels. In my opinion the G3 has the perfect length barrel. I have g3 barrels in my P90, SR47, the other G36 and a couple other guns. When you pull the trigger and the piston slams forward compressing that air you get a very violent turbulent reaction. All of this compressed air blasts out and hits the bb pushing it past the hopup which starts it spinning. Some distance down the barrel after that the bb is going to be moving at its terminal velocity. The advantage of a longer barrel or a tightbore barrel is that it holds the BB in that trajectory for a longer time. Basically it removes some of the erratic behavior of the bb. To test that compare a g3 to a Mp5k. The K will spray BBs everywhere wheres the G3 puts out a beam of bbs.

From what I have seen the single greatest effect on the FPS of your gun is the level of your technical expertise. You can take the best parts in the world, slap them together and still have a gun shooting stock velocities. You can also take a new M120 and get a gun shooting consistantly 410 to 420.


What's better, a long barrel or a short one? For the most part a longer barrel works better than a shorter one. Why? Well aside from the obvious explanation that a longer barrel will be more accurate many people don't realize it'll also give you more power and velocity. When the air is compressed in the cylinder it creates pressure which leads to force. Pressure, P, is the force acted on an object, F, per unit area, a.

P = F / a

Force equals mass times acceleration, F = MA. The mass of the BB doesn't change as it travels, so all of the force goes towards acceleration. All objects move in a constant speed (even if that speed is zero) in a single direction unless force is exerted on the object. When force is exerted the speed or velocity will change, meaning there is acceleration. Acceleration is the change in velocity over time. If a car goes 30mph on the street and speeds up to 35mph in 5 seconds, then 40mph in 10 seconds, it is accelerating by 1mph per second. When acceleration stops, that does not mean the object stops moving. In the case of the car, it remains at the final constant speed of 40mph.

So pressure results in the acceleration of an object. This acceleration is proportional to the cross sectional area of the object, and inversely proportional to the mass of the object.

P = MA / a

Ok what's that have to do with barrel length? The more time a force is exerted on an object the longer it will be accelerated, and the more it accelerates the faster it will go in the end. Obviously a BB will take longer to travel down a long barrel than a short one, thus it will have air pressure exerted on the BB for a longer amount of time and that means more time to accelerate. This is why you will get more velocity from a long barrel than a short one. Example: a SP110 spring in a M4A1 will give a velocity near 390fps (depending on what other parts are installed), but that same spring in a MP5K will only give 300fps.
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HOWEVER, electric powered airsoft guns get their pressure and force only from the air being compressed in the cylinder. It is a specific volume of air that once compressed will want to return to its original volume. Therefore, if the volume of the barrel is larger than the volume of the cylinder than you will get a suction effect in the barrel. Let's say your piston and cylinder will push out 40 cubic centimeters of air and your barrel volume is 60 cubic centimeters. Your piston only has enough air to push the BB two-thirds way down the barrel. Two-thirds way down your BB will reach its maximum velocity and will travel on inertia alone. But in that last third the BB will act like a piston in reverse as it goes down the barrel and cause suction behind it. This suction will want to pull the BB back to its optimal position, two-thirds way down the barrel. Fortunately the BB will have enough inertia to still shoot out, however it will have a lower than optimal velocity because of the suction caused in the barrel will pull it back. In this respect a barrel that is too long will not be good. As an example the HammerMods.Com crew and I experimented with putting a PSG-1 barrel in a M16A2. The A2 was upgraded to shoot 400fps with the A2 length barrel. But with the PSG-1 barrel it shot only slightly over 320fps. Obviously the PSG-1 barrel was too long for the A2 piston and cylinder. Just as a side note the M16A2 has a full, non-ported cylinder, meaning it pushes out the maximum amount of air for version 2 mechboxes.

What does that last statement mean? The cylinders in many of the AEG's have holes in them. This is to port out air. Why do you want air ported out? Well, the concept of force being exerted for a longer time leading to more acceleration is at work here, too. The spring in the mechbox exerts force on the piston making it accelerate. This means that the piston is moving slow in the beginning of the piston stroke and fast at the end. Let's say the barrel has a volume of 20 cubic centimeters. If the cylinder contains 40 cubic centimeters of air you only need to use half of the air inside. To get the optimum performance you want the fastest moving portion of the air, the second half (remember, the air accelerated at the end of the stroke will be moving faster). The first half of the air being compressed is unnecessary because it is moving too slow and will push out the BB before the faster portion of air will even touch the BB. So to get rid of the first half a hole is made in the cylinder to let the air out before it is compressed.


The cylinders in many of the AEG's have holes in them. My friend and customer experienced this problem when his friend installed an AK-47 full tune up kit in his AK-47B Spetsnaz. This included an AK-47 bore-up cylinder and piston head. He gained a substantial increase in velocity but when he finally checked it on a chronograph it showed lower than expected readings. He told me about what was done to his gun and I advised him to switch his bore-up cylinder to a ported MP5 standard bore cylinder (with matching heads and nozzle). He took my advice and we switched the parts out. This change alone resulted in a 20-25fps increase without changing the spring.

So if you want the most velocity for your parts you should use a long barrel. However, if you do not have a cylinder that matches your barrel you will be losing velocity. So before you put a AK-47 barrel on your MP5, or a SG-1 bore-up cylinder in your G3 SAS, stop and think about what you need to do and how it will affect your performance.



Bore up and Silent Piston Head's SUCK!

I'm not saying that the idea of larger bore being beneficial is wrong, but the shapes of the piston heads are all wrong. The convex head leads to turbulence and lower fluid flow rates. This is why:

Friction is everywhere. Even air has friction. Friction leads to deceleration in moving objects. As air moves down a tube the air molecules have friction against the sides of the tube. This slows the air near the walls of the tube while the air in the center moves faster. This in itself results in a convex flow of air as it travels down a tube.

This causes turbulence because air molecules will feel faster flow near the center of the tube and slower flow on the outer perimeter. When you have an object moving at a faster speed on one side than the other you will experience rotation. This is like how tanks steer, by moving one track faster than the other the tank turns. And when objects spin they want to change their trajectory. Imagine your gun with too much hop-up. The bb's are spinning too fast and end up curving rather than shooting straight. This is exactly what happens to the air molecules; they curve out towards the walls of the tube instead of moving straight down the tube.

The amount of curve in the convex shape of the airflow determines the amount of turbulence. This is because the difference in airflow velocities on opposite sides of the air molecules is greater. The greater difference causes more spin. Using a convex piston head increases this curve and causes more turbulence. This results in inefficient airflow.

Why do they make convex piston heads? Well because tapered cylinder heads help reduce turbulence and [dumb] people feel believe that the curved piston head will help use all of the air in the cylinder instead of leaving a small portion of unused air in the cylinder head. If [dumb] people don't believe what I explained about turbulent flow then maybe they'll believe that you'll have more air volume with a flat piston head (which you do but that is unusable tidal air volume that won't do anything). But who knows, people believe anything they read on the internet no matter how dumb it may be.
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