Airsoft upgrades and reliability

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Modifying an AEG can provide some much needed performance improvements, but what does this do for the life of your airsoft gun?

I’ve been told that just by opening a mechbox the chance that something goes wrong goes up exponentially. Why is this? Can I do anything to change that?

 

The short answer is, not necessarily. 

In fact, many times with the cheaper Chinese AEGs I have seen significant improvements to reliability after opening and upgrading the mechbox. Obviously, not all upgrades go as smoothly as expected and there is always a chance you’ll have to open it five more times to get it right. That does happen, even for someone that has performed the exact same upgrade hundreds of times before without a single problem.

Keep it simple. More is less, most of the time.

Some people have a tendency to want to replace everything inside the mechbox believing it will magically create the perfect weapon. In most cases, the more you add, the more likely you are to create new points of failure. The large number of manufacturers today who produce airsoft mechbox components also adds to the complexity of choosing parts that work well together. So, especially for people new to upgrading, I highly recommend starting with the basics (spring and bushings). More does not always equal better.

 

What, if anything, do I have to upgrade in my mechbox to support an M120 spring?

 

In my opinion, the following is required: 

  1. Metal bushings.
  2. Reinforced (higher quality) gears.

The most likely failure point with a stronger spring will be the gears or the piston. A wobbly gear (due to a loose bearing) can lead to stripping of the gears. The safe bet is to add the bearings and a set of new gears. Not all gears are created equal. Ideally, buy gears and bushings from a reputable manufacturer such as Systema, Guarder or Prometheus.

For improved performance: 

  1. Ball bearing spring guide.
  2. New piston and ball bearing piston head.
  3. Consider a more powerful battery.

The ball bearing guide and head will allow the spring to rotate smoothly as it compresses and decompresses. A smooth rotation will reduce binding and twisting, giving the mechbox a slightly better ROF (rate of fire) and better durability. You might get a little more life out of the mechbox by adding a new piston. The fresh grooves on the piston will to mesh up with your new gears, again reducing the chance of premature failure after an upgrade. For most AEGs, the M120 will definitely slow the ROF and decrease overall battery life, so a slight increase in battery mAh or voltage may be necessary.

The key is to realize that everything is connected, so what starts out as a “simple” 400FPS (feet per second) upgrade can quickly become an expensive chore of adding more parts than originally planned. As stated in the first question, simple is usually better and more reliable. Something to consider before planning your upgrade.

Note: The M120 is usually fine for most mechbox designs, however the V2 box has some weak spots. Don’t be surprised if a fracture develops at the front of a V2 mechbox. There are some ways to prevent that, but I’ll save that for a future article.

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17 Comments


  1. You mentioned a fracture at the front of a V2 mechbox, that happened to me, in my TM M4 RIS, and it was completely un-upgraded. It was also less than 4 years old, and only skirmished with once. However once the plastic body broke, I was going to buy a metal one however when I removed the mechbox it had a giant crack in the front, and shortly thereafter literally disintegrated. The piece that was cracked broke and the spring popped out of the side. Any ideas why this happened to gun that hadn’t ever been opened?

    by Logan January 26th, 2009

  2. I’m guessing it happened because of the stress of the piston smashing against the front of the box repeatedly (normal operation).

    That’s the _motion_ that caused it. The _reason_ for the box failing and cracking is either due to poor quality of the box, or (rumoured) because of too much blank-firing, giving less resistance to the piston and thus increasing the force of the smash.

    by Glader January 27th, 2009

  3. In my case, stronger gears of the original gear ratio was not enough to pull back an m120. Can I test if this is a battery problem without buying a new battery?

    by andrew January 27th, 2009

  4. @ Andew, sometimes the M120 is just too much for smaller cell or low mAh batteries, especially 1500mAh stick batteries, etc. Options for testing: (1) borrow a battery from a friend (2) fully charge your battery, it *should* turn the gun over at least once or twice (unless of course it’s an old, worn out 600 mAh 8.4v or similar)

    by 6mm January 27th, 2009

  5. @ Logan, it’s not unheard of to have a stock (un-upgraded) TM V2 mechbox case crack or fracture for no particular reason. You mentioned the broken plastic body, there’s a good chance whatever broke the body *might* have caused the fracture in the V2 box. Did someone fall on the gun or drop it hard?

    by 6mm January 27th, 2009

  6. No, but some stress was on the delta ring because it was hanging on a gun rack, one peg under the stock, one under the RIS. One day I picked it up and, I was holding both piece separately. The delta ring just fell out of the upper receiver, which broke the plastic apart. But it was never dropped or fallen on, only once and that was a long time ago it fell when it was leaned on a wall, cracking the carry handle. Another reason the body MAY have broken, is that my friend carried it by the carry handle, and when I saw him I told him to stop but it was too late. The rail on top came loose, and I think that’s why the body failed eventually.

    by Logan January 28th, 2009

  7. Hey Cpt.LURK from Hazard Strike Force (TN)
    I’ve got a classic army M16 with a upgraded piston and a 120 spring. Just asking for a warning of any parts that might break over time. My bushings look fine and I’ve been playing Bad Karma games(TN) for a year now and haven’t seen any problems. Usually for me when something works good for a long time its about to break. If i get metal bushings will i have to change the number of shims on my gears because that’s what worries me the most about upgrading.

    by Cpt. LURK March 7th, 2009

  8. Hello, i am not new to airsoft, but fairly new to upgrading airsoft guns. and i am about to get a JG AK-47 RIS. Not the JG AK-47 Tactical. And i think the only upgrades i will get for it will be a tightbore barrel, because i think if i just install that i wont have to install more stuff (bushings,pistons, etc.) Plus, it will upgrade my accuracy and maybe fps. So, basically i would really be happy if someone could tell me how to atleast install a tightbore in my JG ak47 RIS.

    by Ryan March 22nd, 2009

  9. So at the beginning of the article, you said that it is not necessary to upgrade every part of the gearbox, however as you get farther into the article you start recommending replacing most of the parts. What is with this contradiction?

    by e1m4user April 18th, 2009

  10. how about a black metal gearbox from a JG mp5?

    by captstar May 1st, 2009

  11. I’m hoping to get my hands on a JG replacement gearbox soon. We’ll let you know how they test out.

    by 6mm May 1st, 2009

  12. You mentioned at one point that the AUG, AK 47 and the G36C were the only guns that were different in terms of the V3 Mechbox. I’m currently looking for a reinforced mechbox for my TM G36C, and I’m either finding Gun-specific mechboxes like the MP5 (which is still V3), or finding General V3 Reinforced Mechboxes. Do you know of a manufacturer that makes a Reinforced G36C mechbox, or would any reinforced V3 Mechbox work?

    by Steve June 28th, 2009

  13. just a question…

    how tough is the stock TM M4A1 gear box?

    by IndusGoth July 28th, 2009

  14. if i bought an sp140 spring and a li-poly batt for my ics m4a1, should i change my gears for newer ones? already replaced my piston to full teeth, metal bishings, shims and piston hesd. and is it very important to change also my spring guide?

    by patrick August 13th, 2009

  15. Hey Steve, you mentioned that a JG G36C V3 Mechbox is different from the General V3 Mechbox? Could you explain some differences because I have a JG G36C V3 and a lot of people’s hop-ups are getting messed up after opening up the gun, and I’m wondering if it might be because the Gearbox is different and it’s causing damage to the Hop-up because of different “Mechbox opening steps?”

    Could I get a response to my question, I’m planning on upgrading my JG G36C with a few hundred dollars in upgrades and I don’t want to mess up what’s going to be my most expensive gun ever.

    by Zing200 September 2nd, 2009

  16. what dieameter bushings would a m14 take ?

    by shane September 30th, 2009

  17. Hi, i have an Ak47 from G@G armament. Can someone provide me with a list with the necessary upgrades for 135 m/s? I am kinda new to airsoft, and i want to purchase what’s better. Thanks.

    by Chris December 1st, 2009