Just another AK-74M on the outside
Content and pictures: Khvarrioiren#1688
Copywriting and hosting: Mahonen#0603
Around a year or so ago, I got more deeply involved in GBBR platforms, namely Viper Tech AR's, and started wondering about the lack of equivalent quality AK-platform offerings. So I searched around for owners of different manufacturer GBB AK's and ended up with a GHK AK74M, a WE AK74M, and a KWA AK74 to fiddle with and look around.
After spending hours upon hours delving deep into the three competing systems, I was mostly underwhelmed by the WE and KWA internal design, both of which have weird design quirks that are by large unnecessary or overly complicated. On the other hand, the GHK design showed the most potential as an internal system that can perform as stably and reliably and is by large an analog of the real steel system apart from dimensional oddities.
Having my firearms experience of my early years significantly molded by my grandfather, a stoic AK enthusiast of several decades, I've got a pretty solid handle of what makes an AK tick the way it is supposed to. After multiple years of creating high-end airsoft builds, I felt I had a pretty good idea of how to translate that knowledge into a GBB rifle. Not just another GBB rifle at that, but something that can and will be used as a military training weapon.
Custom pins
But herein lay an issue I was having a hard time dealing with; a GHK AK is by itself a pretty nice gun for airsoft shenanigans, but at numerous points, it is a platform that has several pitfalls I found to be unresolvable. While dimensionally pretty close to an equivalent firearm, the weight distribution is very wonky compared to an actual AK; the receiver material is mild steel, with an oxidizing coat that prevents rust very well. Still, once you get a rust spot around the rivets, it's just a matter of time when big problems will come up. Another point is that the barrel is screwed onto the trunnion, making possible maintenance in adverse conditions a significant pain. Screwed on magazine catch is another potential, albeit unlikely, point of failure.
At this point, I once again thought, where would we be if VFC made their AK's in GBB form and those years ago. So, inspired by this train of thought, I grabbed my vernier caliper and headed to my outdoor storage, wherein lay the first batch VFC AKS-74N and started measuring things and making mental notes on what would it take to pull off the pretty goofy idea of making a GBB rifle out of an AEG one.
Pinned front trunnion because faffing with Allen keys is not fun.
The two significant differences between an AEG and GBB receiver are the rear trunnion and the outer barrel. AEG receivers' rear trunnion lacks the topmost part where the recoil spring guide sits between a steel dovetail and acts as the top cover's locking mechanism. As a result, the plastic nozzle chamber also had to be modified.
The first idea was to remove the AEG rear trunnion and replace it with a real steel trunnion. This is feasible since VFC's receiver width is only half a millimeter or so more than an actual 74's inside receiver width, and the rivet pattern is identical. The issue, of course, would be riveting the new trunnion in, which isn't something you can very quickly do, so I started thinking of alternatives. I ended up machining a piece matching the shape of the missing part of the trunnion and TIG-welding it to the original trunnion.
Rear trunnion, machined out of 34CrMo6 by Ahola Industries.
While it wasn't a pretty solution, it is by all measures an almost indestructible one. Arguably the hardest fabrication part is by this point dealt with.
Cool beans on the makeshift TDC
The next issue was the outer barrel; as the GHK hop up sits inside the front trunnion and the outer barrel, some pretty radical work had to be done on the outer barrel. What I did got a 12 pack of beer and started dremeling. After some time, it was done. Not pretty, but it works.
Measuring the headspace and the position of the nozzle chamber was a bit of an issue because the VFC front trunnion is shaped with a feed ramp, while the GHK one is a flat block. Filing and dremeling the lower part of the nozzle chamber to fit the curvature, I marked up the holes on the trunnion and drilled and tapped M3 holes on either side and screwed it on. Successfully. The hop-up is pressed against the nozzle chamber by a spring that is pushed against the outer barrels' inside chamfer. The GHK hop chamber is usable, but the adjustment is an ass, as the pressure is always slanted to the right. Reaming the inside flat, filing a Maple Leaf S-hop nub to fit, and creating a ghetto TDC, it's a somewhat serviceable system until I can get my hands on an A Plus hop chamber.
The trigger and fire control group was a relatively uneventful stretch of work. The hammer and auto sear needed to be filed narrower to fit the bolt rails that go down the entire height of the receiver. GHK pins were a no-go since their locking side is 7mm in diameter, whilst VFC has the RS dimensioned 8mm pinholes. Due to this, I experimented with Sako RK pins until I got all the internals to work as intended and got a set of custom-made pins made afterward by Ahola Industries, who also made the rear trunnion addon piece.
Note the auto sear, which had to be filed thinner along with the carrier cam to stop the hammer dropping well over 7mm before the nozzle was in battery.
Internally the system is basically 100% GHK, with custom pins and some minor modifications here and there to make the whole batch work with a real steel pin pattern. The original GHK parts used in prototyping will be replaced with RA-Tech and various real steel parts. With the 1J nozzle and 300mm 6.08id Lamba barrel in place using .32g Tippmann BB's and using Nuprol green gas, the muzzle energy is around 1.2 joules with slight variance unless you full auto it to freezing point.
Scaling up with the stock nozzle, a 400mm 6.05 id Lambda barrel, and .40g BLS BB's, the muzzle energy is north of 2.8 joules on propane, which isn't a bad thing. Remember, the whole point was to build a training weapon.
The VFC trunnion and receiver accept AK handguards without modification.
Externally the gun is at this moment a mish-mash of Izmash 100-series bits like the handguards, magazine catch, barrel pin, and rear sight. Stock is a Cyma one because it a clone of the VFC stock and fits perfectly, and is stupidly strong due to the thickness of the plastic. The pistol grip is an Ares slim AEG grip I used to measure the hole placement for the grip screw bolt and will be replaced by an Izzy 100-series one as soon as the Finnish postal service wants to go to work again.
Cyma stocks also have Izmash markings, in case you haven't noticed it.
Zastava recoil spring used with the higher joule output setup
I am also planning to make a video that goes a lot more in-depth about the build, and I'm working on extensive documentation that has all the parts and their measurements listed if you ever want to do this kind of thing yourself. All of the modifications apply to Cyma, Dboys, and VFC AKs.
I want to thank Ahola Industries for all the custom parts, Yaroslav B. at Kalashnikov Concern for helping me get specific measurements, and Luisu's Garage for the welding and metalwork.
