AEG Upgrade/Tuning Guide

Quotation & Reference: 

Article from Zi. Wan (AKA Pestobanana from ASC)


People constantly ask me what they should upgrade in their AEGs. I do my best to respond, however the answer is always very similar, and I'm getting tired of typing the same stuff out over and over again. Instead, I'm going to write out my basic thought process when dealing with clients so the community can read it, and I can link a thread instead of typing everything out. This is not a guide on how to perform the upgrades, this is also not a 101 spoon feed. This is for people that already know something about upgrades, and helping them to decide what to do and what parts suit. Do not attempt stuff if you have no idea what you're doing. I will try to keep this write-up short (as much as possible) and to the point.


Have a plan before you start doing stuff. Assess your performance priorities and budget.
-If you upgrade without a plan, it will run like it. Have a plan.
-Open the gearbox if the internals are unknown, if they are brand new, use a google image search as a guide.
-Figure out what needs to be replaced, why it needs to be replaced, and what parts to replace with. If you blindly upgrade parts without reason, you are simply getting satisfaction out of wasting money.
-If you intend to upgrade in stages, plan ahead and take logical steps. For example: if you are planning to fully upgrade your gun in two stages and you are paying someone to do it, make one stage the barrel group and the other the gearbox so you aren't paying overlapping tech fees.

Performance vs. Preventative Upgrades

Different upgrades do different things. Some people like to tinker, some people value their time. This can change upgrade priorities.

Performance Upgrades:
-Will change something that is tangible when you shoot
-Includes accuracy, gearbox noise and efficiency, rate of fire and trigger response, etc.
-Shimming, changing gear ratio, barrel and hop up upgrades, air seal upgrades, MOSFET, motor upgrades, etc.

Preventative Upgrades:
-Non tangible, no difference in performance, but reduces likelihood of failure and gives peace of mind
-Any case of replacing one component with an identical but higher qulity one: gear set, gearbox shell, piston, cylinder head, tappet plate, etc.

There is some overlap. For example, shimming improves efficiency but also prolongs the life of the motor, gears, and trigger contacts if you do not have a MOSFET.


This is a topic people do not understand and people like to spew random made up numbers about. People don't even understand these terms.


How far you can shoot a BB with a relatively straight trajectory. This means no cranking the hop up or shooting like artillary.
-The ONLY contributors of range are BB velocity, amount of backspin, and BB weight.
-Hop up does NOT affect range unless your existing hop up is unable to provide enough back spin to lift your desired BB weight.
-FPS consistency is directly related to range consistency. You do not want BBs falling short or shooting further than average. This will not affect your horizontal groupings. That's right, R Hop does not actually give you more range. It only gives you better groupings at range.

Groupings. Doesn't matter what the trajectory is like, just groupings at certain ranges.
-Barrel quality, hop up performance, BB quality, FPS consistency. This means that all platforms have the same accuracy potential as long as the FPS consistency is the same. That's right elitists and fanboys, HPA, AEG, and PTW all have the same potential for accuracy.

Related Upgrades:

Barrel Group:
-Pick a high quality stainless steel barrel. Otherwise, just run your stock barrel. "Budget" barrels are cheap and offer very little if any performance gains over a stock barrel. I use PDI and Prometheus barrels exclusively.

Hop Up:
-Unit doesn't matter as long as it works - it is just a housing. There is no benefit in upgrading to a metal hop up unit aside from durability. If the adjuster likes to slide loose, shove a small O-ring underneath it and it will be tight.
-If a hop up rubber has a standard mound inside and is not of obviously poor quality such as King Arms, it will shoot more or less the same. This means that OEM rubbers such as G&G, VFC, TM etc. will shoot more or less the same as aftermarket "upgrade" rubbers such as Prometheus purple, Lonex, etc. If there is a design difference, then there will be a noticeable difference eg. PDI W-Hold.

Air Seal:
-Replacing a component does not guarantee better air seal. The original part must be leaky for there to be a performance gain.
-These are the points of leakage: piston head - cylinder, cylinder - cylinder head, cylinder head - nozzle, nozzle - hop up rubber, hop up rubber - barrel.

Rate of Fire/Trigger Response

These two generally come hand in hand, though it is possible to build a sub 30 RPS gun with good trigger response. Trigger response is the time from motor startup to the BB being fired. Aside from using an 11.1, there are three main factors: motor, gear ratio, and electronics.

Where To Buy Stuff:

Airsoft Parts Canada
Airsoft Store Canada
Black Blitz Airsoft (most of the internals here were sourced upon my recommendation)
Brill Armory (California)

Parts Selection:


-Barrel length does not have much of an effect on accuracy. Barrel quality does.
-Having tested PDI 6.01, 6.05, and 6.08 barrels of the same length, I did not notice much of a difference in terms of accuracy. Though, I remain unconvinced of the theory behind wide bore barrels.
-I use PDI and Prometheus exclusively. It is simply not worth it to get something cheaper because there is not much performance gain over a stock setup. Other "high end" barrels tend to be full of bullshit gimmicks (Miracle barrels) or are brass.

PDI vs Prometheus:

-I have used dozens of each and I've probably had a hundred of them pass through my hands by now. I have not noticed a discernible difference between the two.
-Not all Prometheus barrels are the same. Most have straight hop up windows, but some lengths such as 318 and 433 have slanted windows with O-ring alignment channels at the front.
-Prometheus is easy to R Hop. PDI is significantly more difficult to R Hop. I do not recommend trying it yourself, and there are very few people in Canada that actually know how to do it properly. Do not half ass it, you will look stupid and it will not perform well.

Hop Up:

All of my guns are R Hopped. I do not use anything else. In my eyes, there are only 4 options when it comes to hop up: stock, PDI W-Hold, flat/bridge hop, R-Hop. My go to hop up rubbers for standard setups are VFC stock, G&G stock, and Lonex 50D.

PDI-W Hold:

-Best plug and play setup.
-Drops 30 or so FPS due to the channel between the two mounds.
-Helps centre the BB in the hop up.

Flat/Bridge Hop:

-I refuse to install these unless the client already has a drop in kit. The reason is the amount of work for me to modify the setup to a flat hop is pretty much the same as me R Hopping it.
-Drop in kits are available, flat hop mod is not difficult. Pair a moundless rubber such as Prometheus or Modify, then use the Prometheus flat hop nub or bridge hop nub.
-Provides more lifting capabilities and more consistent hop due to the larger surface area. Bridge hop also helps to centre the BB in the hop up.

R Hop:

-This is what I use in all of my guns, and I strongly encourage it for everyone else as well. Currently the best hop up setup available.
-It is a modification of the barrel window and is non transferable between barrels. Do not pay to have this done to a shitty barrel. Do this after you have a good barrel that you are happy with.
-Very simple if you are good at it, rocket science if you are not. If you do not understand the process or purpose, please do not attempt. Pay someone else to do it and you will save hours of time, money on the kit, and a potentially ruined barrel.
-You will not see the benefits if you use light BBs. I recommend .28 or heavier.
-It is perfectly acceptable to use your stock rubber and hop up unit for this, as the rubber only exists as a seal. This will help mitigate chances of hop up and nozzle alignment issues.
-Different hop up units have different internal diametres, different hop up rubbers have different thicknesses. Mixing aftermarket parts can result in compatibility issues, so this is another reason to keep the original setup.

In short, barrel group upgrade flowchart looks like this:
-Hop up first, unless it is non transferable, then barrel first.
-If it is transferable or you don't intend on getting a R Hop done, get a hop up first and then get a barrel.
-If you do intend on getting a R Hop done, get a barrel first, then get it R hopped.

Gear Set and Motor:

My philosophy for guns under 500 FPS is to get the highest speed gear set available to you, then use the motor to reach the desired rate of fire. However, there is no point in changing the gear set unless you have a neodymium magnet motor, so upgrade that first. Ideally though, you would want both at the same time.


With the exception of stock gears, I only recommend using Siegetek gears and SHS gears. Modify and Lonex gears are common, they are worse than SHS gears and are twice the price. Prometheus gears are good, but are nowhere near as good as Siegetek, and are almost as expensive. It is also very important to pair the gear set with the pinion, its a gear too.

-Siegetek gears are CNC machined out of chromium molybdenum steel rods, and the pieces are welded together. SHS and all other AEG gear sets are made of individual pieces of sintered steel. Shafts are pressed through, pieces are held together by rods, screws, and friction. Cheaper gears that look machined are machined, but out of sintered steel.
-Do NOT use Siegeteks unless you are very good at shimming.
-For gear ratios, lower numbers are faster, higher numbers are slower but provide more torque
-18:1 is standard gear ratio, unless you are exceeding 500 FPS I see no reason to exceed 18:1.
-12:1, 13:1, and 16:1 are resultant from different cuts between the step (spur) and sector gear. They all use the same bevel gear. 16:1 and 18:1 the only difference is the step/spur gear, same for 12:1 and 13:1. 12:1 was originally made out of 13:1 by taking the bottom half of the step/spur on a 16:1 set and pressing that on to the step/spur on a 13:1.
-10:1 and 14:1 are cut bevel - step (spur) gear, they use the same sector gear.
-Do not upgrade the gear ratio unless you have a neodymium magnet motor.


-TPA = turns per armature
-Most stock motors have shitty magnets. Do not buy an aftermarket motor unless it has neodymium magnets.
-More speed = less torque. High speed high torque motors do not exist, this is just marketing bullshit.
-Motors are more complicated than this, but in short, more TPA is more torque, less TPA is more speed.
-Unless you are trying to build an extremely high speed gun above 50 RPS, speed motors are pointless.
-Most motor labels are inaccurate. Most torque labelled motors are actually balanced motors. SHS and Lonex Torque motors are balanced motors. ZCI high torque is actually fairly high torque. Tienly 30k is also high torque. Frankentorque and ASG 28 TPA motors are extremely high torque.

There are four gear set and motor combinations that I like to use and would recommend. They all provide very good trigger response.

Siegetek 10:1 + Tienly 30k with Siegetek Pinion:
-One of my favourites. Nets you roughly 40 RPS on a 400 FPS gun using a buffer tube 11.1.

Siegetek 10:1 + ASG 28 TPA with Siegetek Pinion:
-Very efficient. Nets you roughly 30 RPS on a 400 FPS gun using a buffer tube 11.1.

SHS 12/13:1 + SHS High Torque:
-Runs very smoothly. Nets you roughly 40 RPS on a 400 FPS gun using a buffer tube 11.1.

SHS 12/13:1 + Frankentorque with G&G pinion or SHS Pinion
-Runs very smoothly and efficiently, Nets you roughly 25 RPS on a 400 FPS gun using a buffer tube 11.1.


16 AWG wiring, nothing thinner please. Most places that sell MOSFETs will also sell wire. Some MOSFETs come with wire anyway. A MOSFET is recommended in all guns. It prevents trigger contact failure and improves electrical efficiency. Some are also capable of burst functions.

I ONLY use BTC FETs and home brew 3034 basic MOSFETs. Gate units are very common in Canada. They look very nice and presentable, however they take up more space than they need to and are quite fragile. I do not recommend them, though if you are looking for a burst timer I suppose that is the only easily obtainable option. If your AEG has a microswitch trigger, you are also limited to Gate FETs unless you source a debouncer for a non microswitch compatible FET.

Simply put, if you can't get a BTC, get a 3034 FET.

Aftermarket trigger assemblies and switch systems aren't really better than stock parts. Often times they lead to compatibility issues, so I recommend keeping the stock trigger switch and using a MOSFET.


Piston upgrades are preventative upgrades. In my opinion the best pistons are SHS, Lonex, and Prometheus. Other pistons have design issues or issues with the metal hardness. Avoid all pistons that are transparent or translucent. Pistons with only a metal release tooth are more prone to failure.


-Full rack of steel teeth.
-Pre lightened seven hole version available.
-Best general purpose piston. I still use these in half of my guns, and is the only piston I buy by the dozen. If you're undecided at all, just get this.
-More forgiving to inexperienced users. Since it has a full rack it is more forgiving in case of pre-engagement. First few cases will only cause surface wear but will eventually cause the rack to shear off the back of the piston. A half rack piston will suffer extreme deformity of teeth on any instance of pre-engagement.
-Good enough for all sub 400 FPS builds
-Despite SHS quality control, I have never seen a piston fail due to poor QC. Only user error or extreme stress. I killed one with a 70 RPS DSG.

Lonex and Prometheus:

-Extremely resilient steel teeth and tough body, I do not anticipate seeing either of these fail under normal circumstances.
-I recommend these for experienced users and guns that are not high speed builds.
-Highly recommended for high FPS builds

Piston Head:

-Avoid all piston heads that are made of more than one piece. Avoid mushroom style AKA silent piston heads.
-Bearings are optional. If you have a bearing spring guide, don't use the bearings, just use one of the metal washers to mount the piston head.
-Also avoid polycarbonate piston heads such as Modify and Guarder. Polycarbonate is brittle and not flexible enough for repeated impacts.
-I only use POM piston heads, though aluminum ones are fine for sub 25 RPS guns. Aluminum piston heads are all more or less the same. My preferred two POM piston heads are Lonex and Prometheus. Lonex is technically two pieces, but they aren't disks screwed together like most shitty stock piston heads.
-If you have a one piece piston head and it is leaking, check for damage in the O-ring channel. If there is no damage, replace the O-ring.


Any stainless steel cylinder will do. My preference is for ZCI or SHS. Stuff like "anti heat" etc are gimmicks. Avoid coated cylinders such as Lonex and Modify. The coating wears away and once it does it will destroy your seal.

Cylinder Head:

As long as it is metal, it doesn't really matter. I prefer Lonex, SHS, and Ace1Arms because it is easy to remove the original rubber washer and install a sorbo pad.

Stock plastic cylinder heads are not THAT bad, but they do usually break after a few years. Usually not a must replace scenario unless the O-ring is too under sized to seal with the cylinder.


-Material does not matter
-Double O-ring is a gimmick. They are not bad, but there is no benefit.
-The only important thing is that there is an appropriately sized O-ring inside, and that it does not wobble too much on the cylinder head spout. Make sure that it does not leak, and make sure that it is not so tight that it gets stuck on the cylinder head.
-My usual go to nozzles are SHS and Lonex. Surprisingly, SHS has better nozzle QC than Lonex.

Tappet Plate:

-Most stock tappet plates are fine
-If you really want to replace it, just get SHS and make life simple. They are my go to tappet plate. I've probably used 100 if not more and I do not recall ever seeing one break under normal circumstances.

Spring Guide:

-Does not matter as long as it is metal and has bearings.
-Plastic ones will break at some point.

Bearings vs. Bushings:

-6mm and 7mm gearbox? Don't even think about bearings. Get steel bushings ASAP.
-8mm bearings are okay, but will still inevitably break. I spent time experimenting with bearings, but they all ended up breaking over time.
-I have yet to see a 9mm bearing break, but that's because very few gearboxes use that size.
-If you absolutely must sacrifice reliability for a marginal performance gain, get Modify ceramic bearings.
-Never run a bearing underneath the spur gear. It will be the first to fail. Next is the one underneath the sector gear. All other bearings should last a while if they are 8mm.
-If you need aftermarket steel bushings, SHS bushings are not bad, they do the job. My only complaint is they are thicker and can sometimes cause issues in thinner gearboxes.
-Lonex and VFC 8mm bushings are the same, they are my preference for 8mm bushings.

Gearbox Shell:

Unless you have a shitty G&G gearbox shell where you know the front is going to blow off, there is very little reason to upgrade the gearbox shell. QSC gearbox shells exist, if you like that function then by all means, upgrade. If you are building a gun that is above 500FPS, then yes you may want a CNC machined gearbox shell for durability. All of my guns run stock gearbox shells. I have never seen a gearbox shell break when cylinder windows are radiused and sorbos were installed.

Pointless Upgrades (my opinion)

-Selector plates
-Safety levers
-Cutoff levers (in most cases)
-Spring sets (in most cases)
-Anti reversal latch unless you somehow broke yours

Related Modifications:

Angle of Engagement:
-Just get it done. A sorbo costs $6.

-If you are doing the work yourself, just do it. In my opinion though, it is not worth paying a guy money to do this unless you are swapping to a better gear set.

Gearbox Radiusing:
-I don't see it as necessary in most setups, but just do it. It only takes a few minutes and doesn't hurt.

Short Stroking:
-Unless you understand what you are doing or requesting, don't do it.

Upgrading in Stages:

It is common for people to want to upgrade something now, then do more down the road. It is therefore beneficial to make a plan and optimize the steps. For example, my goal is to have a fully upgraded gun. I want to do part of it this winter, then finish once I receive my tax return. You would want to pick upgrades that will not overlap. You don't want to buy a SHS gear set now and have to replace it with Siegeteks at the next stage. You will be paying an extra hundred dollars in labour for your tech to do this. Instead, prioritize accuracy. Fully upgrade the barrel group and air seal components. Only perform the minimum requisite gearbox upgrades such as a MOSFET, leave the rest for the next stage. Alternatively, keep the stock barrel group, but fully upgrade the gearbox all at once. That way you are not paying for the gearbox to be worked on twice.

Prioritizing Upgrades:

The first upgrades you do should be the basic preventative ones. Change out the common points of failure. If your gearbox is decent, there won't be too many things. If your gearbox sucks, then you will have to change everything at once, or you can just change things as they break because it may not be worth upgrading.

For example, in a 2012-2014 model VFC the priorities would be:
-Install a MOSFET, preferably 3034 or BTC.
-Replace tappet plate with SHS.
-Replace piston with SHS, Lonex, or Prometheus.

G&P standard would be:
-Install a MOSFET, preferably 3034 or BTC.
-Replace motor.
-Replace piston, piston head, and gears.
-Put a solid steel bushing under the step/spur gear to prevent failure.

LCT would be:
-Install a MOSFET, preferably 3034 or BTC.
-Replace plastic spring guide with a metal one with bearings.
-If it is a version with bearings, replace them with solid steel bushings.

After you have your basic preventative upgrades done, then you can then re-assess your performance goals of accuracy, rate of fire, and trigger response. Find a balance, make your plan, have fun.



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