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KJ Works M4 - Possibly the best performing GBB M4 out of the box?
  • Manufacturer 
     KJ Works
  • Model 
  • Capacity 
  • Weight 
  • Power 
     320fps | 450fps
  • Power Source 
     HFC134a, Green Gas
  • Blowback 
  • Hop-up 
  • Shooting Mode 
     Semi, Full-Auto
  • Construction 


Great gas efficiency
Reliable and consistent fps
Great performer out-of-the-box
Great platform to create a Diemaco GBBR
Can accept AEG parts
Lower cost than most branded GBB M4's
High steel content in the materials used compared to pot-metal and other materials
Stock tube is reinforced from the inside


No trademarks
Unrealistic bolt head
Hop adjustment can be seen above the bolt
Magazines need a specific adaptor to load efficiently
Lack of performance aftermarket parts available at this date.


Despite the KJ Works GBB M4 being one of the last GBB M4's to be released, it is not a copy of any other GBB M4 platforms.

It has to be said that with such great performance as well as being cheaper than some of the alternatives, it's already quite a contender if you were to look to purchase a GBB rifle since this is one of the best performing GBBR's out-of-the-box



In the recent months, plenty of companies and manufacturers have ventured into the GBB market making various rifles and aftermarket parts for the said rifles. KJ have never really been amongst the top of the list when it comes to reliability and availability of parts for their pistol range. People were not sure if it was a wise idea to buy a KJ Works GBBR when some of their pistol designs were not up to their high expectations. Fortunately, Tanio Koba have collaborated with this project and with his design experience and expertise, the KJ/TK M4 has been released. Initial reports for this rifle were grim due to the videos posted on streaming video sites showing the inconsistent rate of fire and the insane cooldown factors their prototype guns encountered. Now that the improved version of this gun is used for production eliminating the previous obstacles, this may be another interesting contender amongst the GBBR's.

Initial impressions.

If you were to buy this KJ Works M4, lets face it... you're not likely to bother with picking into the minute details of its packaging since this is at a price that is lower than some of the higher end GBBR's. But to the surprise of most people, this is actually quite decent. Although it doesn't feature a fancy glossy box with colors everywhere and inside its plain brown box you will see that KJ have only used polystyrene for padding, at least they did not use corrugated cardboard for padding.

Speaking of standing out and looking different, since this gun uses a thermold mag. This is the only realistic Diemaco (Colt Canada) GBBR on the market today. Featuring a thermold mag instead of the STANAG style mag for the gun, it already makes this stand out amongst the rest of the GBBR classes on the market today. Along with standing out, KJ have actually not bothered with putting any trademarks or any markings at all on this gun. So what does this mean? If you're into markings, this actually is an ideal platform to do any custom work on your receiver since if you were to buy another brand of a GBB M4, you will have to replace the receiver with another for a marking of your own choice or source a plain receiver if you wish to have something different.

With most of the gun using a similar design with the rest of the GBB M4's, you're not going to be entering any unchartered territories with using this KJ M4 if you're planning to buy one of these. With everything that's supposed to be made of metal it's metal and to our surprise, using a neodymium magnet, everything from the sears, selector switch, firing pin, outer barrel, stock tube, receiver pin, mag release, delta ring as well as the bolt release latch is made out of a ferrite metal which narrows it down to some form of steel. Don't think this is relevant yet? Compare this with the bolt release of other variants that use pot metal or probably metal looking cheese, the internals on this KJ M4 is designed to last. Props to KJ Works for using proper materials

Upon inspection on the rest of the body, you will also notice that there're a few unrealistic elements on this gun. The hop adjustment turret is actually located directly above the front of the bolt. This may be slightly off putting for those that want the ultimate realism since they follow the GBBR's for this very reason. It's not all bad I'd say since hop adjustment is made much more convenient without having to reach inside the foregrip, under the outer barrel to adjust your hop and neither do you have to remove the magazine or lock the bolt back to adjust your hop settings.

Furthermore on the topic of realism, the nozzle actually protrudes out much further than any other GBB M4's to work along side with its hop up system. Although this is not something you will see during use or notice unless you have the bolt locked back and looked straight at the front of the bolt, you'll know this difference is there. However due to its elongated nozzle, KJ have made the nozzle much thicker as compared to the others to strengthen this part that is a high stress point therefore reducing the chances of a nozzle breakage from regular firing of this gun. Another thing that deserves a mention and if you have one already or have researched into this gun you will know of the 'rubber band' mechanism inside this gun and may be a little put off by it. We can tell you that this is not a vital part of the mechanism and the gun does not rely on this part to perform well. It merely is just a bolt dampener to reduce the excessive stress that may occur during intensive usage of this gun or when used under hot conditions.


Chronoing in at 450fps ±4fps (26celcius ambient temperature) using green gas with slow semi automatic shots, this is very consistent for a gas blow back weapon whilst giving a very nice kick as compared to a slow shove on some other alternatives. With our no-mercy cooldown test, where a fully charged magazine is used on full-auto, reloaded with ammo and fired on full auto again, this gun was capable of expending over 2 full magazines worth of ammo only using one single charge of gas. This test was repeated twice once the magazine returned to the previously stated ambient temperature and gave an average result of 58rounds on this test.

A grouping test was also carried out on the KJ Works M4 using KSC perfect .20g ammo and green gas at 20metres. Without a proper open area to set the hop, we had to make do with the 20metres we have available to do a groupings test with the hop set to what seems correct at this range. A target was printed on an A4 sheet of paper, the shots were able to produce a 4.5inch grouping at prone position. Although it must be said that if this was secured on a gun mount or using .25g ammo, the performance will be much better due to the recoil and the fps causing the .20g ammo to have a less stable flight path. Below is the groupings sheet before and after the hop adjustment.

Groupings before hop adjustment
Groupings after hop adjustment


Despite the KJ Works GBB M4 being one of the last GBB M4's to be released, it is not a copy of any other GBB M4 platforms where the internal designs are specific to the KJ works so all the rumors are proven false regarding this being a clone of another platform. With Tanio Koba working alongside with KJ, this GBB M4 have definitely hit the spot for standing out even without using trademarks on the receiver. Being able to adapt AEG outer barrels, this is another major selling point since plenty of old-timers would have spare front end kits available on their disposal without having to fork out extra money to buy body kits for a new gun. With their hop up chamber designed to have minimal parts and joints, the fps consistency is great due to its incredible air seal in the mechanism.

It has to be said that with such great performance as well as being cheaper than some of the alternatives, it's already quite a contender if you were to look to purchase a GBB rifle. However, knowing how this is possibly the best working GBB M4 out-of-the-box and the fact that the amount of money required to turn this GBB M4 into the high performance category is much lower compared to the others is going to tip the scales back for you to decide if the lack of trademarks and unrealistic bolt and ejection port (hop up turret) is worth the performance. Decisions decisions...