CYMA M4 CQB Basic Upgrades

Looking for some advice to upgrade my CYMA M4.

Just the basics I guess like spring etc…??

Don’t know what to change out, never opened it up before, so let me know what basic stuff I should upgrade, specifically if a spring, what type…???..and any exact detail for other parts.

Thanks in advance.

Well, you’ve come to the right place.
@DocBob Take it away.


Go the alloy double o’ring cyl head/nozzle for starters. If staying nylon gears I wouldn’t really go above a m90-m95 spring, mine went for a little while on a spring from a metal wells box at over 300 fps but inevitably stripped.
Simply stretching the original spring will give slightly higher fps.
Double check your return spring as it may need to be replaced or made slightly shorter.
Get good seals first👍

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I know my time with the CYMA M4 was very interesting. Some things at the time had to be proprietary if you wanted to do the easy mod, but I was a newb and we had stores in SA in those days :joy:
I would agree with BMD, nylon gears do not last long if you go to heavy on the spring tension, I think I will have to dig through my photos and notes. I reckon I used an M100 with the nylon piston assembly and head with a green "O"ring, I also used a CYMA alloy head/nozzle, and a silly 7.1 barrel at 35cm. That later changed to a 7.3mm… :joy: not so squeazy. I still have this gerabox assembly and it is slated for another modified build.

So, this is my first ever modern Gel Blaster, I decided I wasn’t going to be paying some shop to do something I figured I could do and pay a fortune for it as well. Most of the people here were my inspiration and a huge driving force to do this. They had the patience for a new guy asking many dumb questions.

I posted these pictures to show you what I bought, and what I changed it into, after the internal mods, I had an average FPS of 310. As I struck problems, I posted photo’s when necessary and a full description of the issue. It was surprising just how simple the fixes could be sometimes. A screw to tight, or anti reverse latch out of position…remembering these learning curves brings a smile to my face and my eagerness to push boundaries.

One member of the old place was named “Cruise”, he is forever in my mind an innovator of the AEG blasters. I really miss his ideas and discussions but thanks to that Ex Navy gerbil politician in WA, he put an end to Cruise remaining interested in a sport he could no longer participate in. This is what drives all of us, innovation.

I hope you are inspired and not frightened away by looking at the task ahead. A simple trick I learned was to either video or photograph each move I made. Video is good, if you get the right angle and can see what happens when you do something. Good luck, fear nothing and above all enjoy everything.


As mentioned seals first and foremost. Add a spring to get 300fps, an alloy barrel if it dosent have one, and a hopup. A better battery. With these, you will have a blaster thats a good performer.
Down the road, gears, piston, head/nozzle for more consistancy and durability.


Well it used to be a Jund/Cyma M4 CQB I picked up for $75 new :rofl:


As @Bigmuthadrums has already commented, it really comes down to what you actually want out of your blaster?

There’s basically 3 stages of builds that I used to do, which is the same for all blasters, including the CYMA M4 etc.

STG1: Simple air seal upgrades with a better o-ring, piston head and T-Piece blue print along with the appropriate alloy barrel to suit the volume ratio.
Slight spring upgrade and change batteries/plugs for better components such as a TURNIGY battery and DEANS/XT Plugs to suit.

STG2: Cheap metal gears, upgraded piston and piston head, higher main spring, slightly upgraded motor, higher rated trigger switch and wiring to suit, stabilisers for the barrel and hop-ups/muzzle breaks to suit.

STG3: Complete Doc Bob overhaul :flushed:
Completely upgraded gearbox, all Metal/SHS/Shimmed/Stroked/Ported or whatever required.
Highest rate spring to keep FPS at the 300 mark, Motor to suit FPS/RPS requirements, fully upgraded wiring and FCU to suit, plus all the extra add ons for the externals requested.

It’s all about what the customer wanted to achieve with the builds…… a reliable stock blaster, right through to the top end full custom requirements.

Set a target for what you want, then go from there :+1:


Thx everyone for the suggestions.

I pulled the whole thing apart to learn how things work etc…and one of the gears has a crushed tooth, top dead centre…is it easier just to replace the whole body and gears all for metal…costs about $200, but that would solve everything…??

Or would it still need a better spring, seals even in the expensive all metal gears/housing etc…??

Don’t know what I’m doing, but trying to learn…thx.


Hey @cogman , that looks like it’s done quite a bit of work!
Are you running a stock or upgraded motor, stock/upgraded spring & 7.2 or 11.1V ?
Both your pickup and release teeth are quite worn, which is normal in high mileage or higher speed gearboxes.

You will definitely benefit from upgrading to even just a cheap generic set of cast metal gears, motor pinion and steel rack piston.

While you are there, shim it nicely, fit a better o-ring and main spring.

This will have it running like a champ for quite some time ahead :ok_hand:

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Hey DocBob, Thx for the reply!!

Just using the motor it came with. I hardly ever use it except a few times out on the acreage. Don’t play games, so it’s pretty new, BUT as soon as I got it I added a 11v battery, so maybe why the tooth is toast…??

I can’t find all metal gearbox for under $200…??..

a cheap generic set of cast metal gears, motor pinion and steel rack piston
Where would I get that…??

While you are there, shim it nicely, fit a better o-ring and main spring
what type of O ring and spring exactly would I get…??

Thx for the help, don’t know much about any of this, but trying to learn… :wink:

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YouTube and Google is your friend :+1:
There’s many good suppliers in QLD and online overseas.

Recommend X-Force myself, but you can also check out the “Retailers Ranked” thread on here for good businesses near to your location for who to see and who to stay away from!

But the advantage of paying a little bit extra by dealing with a store in Australia is that they can talk to you directly about your blaster, and explain the exact parts that you need, plus give advice on how to fit them :ok_hand:

If you do have any issues, they are only a phone call away to help you out.

If you search YouTube for build videos that are of your particular brand of blaster, they will help you to understand how to pull them apart and fit the upgrades to each required part…… as well as show you how to shim, set motor heights, do wiring, learn about batteries/charging etc. etc.

The more time you spend searching, the quicker you will learn all about blasters and how they operate, which will lessen the amount of questions you will find yourself having to ask :sunglasses:

Highly recommend checking out @BradleyPhillipsYT
There’s not many blasters/nerf products that he hasn’t reviewed, and also @LowGuido for the technical details/guides on how to do the various upgrades :white_check_mark:

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Hey man, if you’re willing, there’s a full metal exterior, full metal internal blaster for 250 that’s pretty decent.

You might need a new battery, or to rewire it, but it’s just a rebranded JG and apparently rock solid.


I second those blasters my mate brought one of the 9” versions pretty solid for the price.

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This actually looks nice. Price is fantastic for what you get.

The supplier runs Corporate Field Events and were selling high quality blasters cheap, even when I was still involved before the WA Bans.

It’s great to see that they are offering these for this really great price for everyone to enjoy :ok_hand:

I would have jumped on these straight away back in the good old days :white_check_mark:

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Gel Blaster GBX-CQB 4012T

Apart from that store that sells them I can’t find any detail online about GBX…??

Is it a rebrand…??

Yeah. Rebrand of JG. The individual blasters have different names too.

They’re these

With different externals and an XT-30 plug.


Ok cool, thx for the reference about it being a JG…soooo…what to do…??

Instead of upgrading my Cyma M4 to all metal gearbox etc for $200

I think I’ll just buy the GBX-CQB 4012T for $220…??

The JG M4 Carbine Gel Blaster is $450…what would I gain by spending an extra $230…??

Thx if you have an opinion… :sunglasses:


I think that the GBX CQB at $220 is an absolute bargain and already has a reputation as a really solid blaster with very few issues :white_check_mark:

Upgrading any stock blaster will easily run into the $200 mark just in parts alone, so better off buying something that is already built for you :+1:


Upgrade that sucker! :laughing:

The thing about upgrading instead of just buying a better blaster is that you learn heaps and have a ton of fun doing it. It’s really our love of modding that’s drawn a lot of us to this forum.

Anyone can buy a great blaster, more power to you if that’s your preference. But that just makes your blaster a matter of money, tweak it yourself and there’s a little bit of you in it. Plus you get the satisfaction of knowing you made an average blaster perform the best it can. :+1: