Double Bell AK mods

Hey all thought I would start up a topic specific to the double bell AK range. Having now modified mine, there are a few tips I wanted to share as well as highlight a couple of issues I encountered and how I overcame them. Hopefully this helps a few of you if you have plans on modifying this blaster yourselves.

The version I have is the AK023 as pictured below

To start, my main reason for modifying this blaster was the challenge of modifying something other than an M4 style blaster, which I had done before. I wasn’t after super high fps or rof just something reliable. I actually was aiming for a drop in fps so it would be field legal and the real steel doesn’t have a high rof either.

Stock specs were 17rps on 11.1v and an average of 360fps before I changed anything.

Stock internal parts of note are:

  • V3 cast metal gearbox (not radiused)
  • 18:1 gears with a very large delay chip on the sector gear
  • 70% ported (port starting at 49mm) stainless cylinder
  • 45cm inner barrel with 7.3mmID and 8.5mmOD
  • 1.4mm main spring

Stock internals

Having taken apart the blaster there were a couple of issues I found straight away.

  1. The ported cylinder was under-volumed for a 45cm 7.3mmID barrel (ve was 1.13 using the gbf volumetric calculator)
  2. There was an air leak between the nozzle and t piece; and
  3. A vacuum was being pulled as the piston was being pulled back.

The ve could be improved to 1.66 with a 100% cylinder and the vacuum issue was due to an oversized o-ring on the piston head which could be easily fixed by replacing it.
I don’t have a pic of of the stock o-ring (I threw it out) but it pretty much filled the gap in the piston head and was not loose as they should be.
The air leak between the nozzle and t piece required an o-ring to be added to extend the nozzle by 0.5mm and get a good seal. The original nozzle was stuck on pretty good so I cut it off, but seeing as these blasters use the same nozzle as a jm gen 8 it was easy to get a replacement.
Extended nozzle

Having thought I had sorted out all the kinks I then started upgrading the internal components and this is when I came up against some more issues.

  1. Both the SHS and bigrrr gears I tried were too tight to shim when the gearbox was closed. From inspection this was due to there being no recess for the bearing lip to sit in and there was actually a raised area around the holes for the bearings which caused them to sit too far into the gearbox (see below image).
    Before sanding
    I ended up sanding the raised part down and replacing the stock bearings with retroarms bushes, which allowed for enough room to properly shim the gears.
    After sanding
    The stock bearings also seemed to not spin very freely, so I suspect they needed replacing anyway.
  2. The piston I originally tried (modify) was binding and not moving freely (noticed that the stock piston was also doing this, but only just). After trying several different pistons I settled on the aztech piston being the best fit however I did take 1mm off the back of it to clear the back of the box/ spring retainer before the piston gets released.
    Modified piston
  3. I also noticed some casting issues in the gearbox. I.e there were some bumps in the piston rails and guides for the tappet that I sanded down smooth using some 600 grit sandpaper
  4. The motor cage was contacting the springs for the motor brushes and would have shorted. I fixed this by grinding out the area that was contacting with a file
    Modified motor cage
  5. The spring retainer was a bit wobbly with the new spring too. To fix this I just used a 10c coin and M3 countersunk screw to secure it against the back of the box. I did have to Dremel out a small amount of material from inside the receiver to make this fit.
    Secured spring retainer

After all this I put the blaster back together however I then was experiencing some timing issues… Originally I had used the stock tappet plate + the SHS delay chip and was getting a drop in fps on auto. I then removed the delay chip and had no fps drop but was having feeding issues. Finally changed to the SHS tappet plate, trimmed the delay chip and it started to work great. Consistent feeding and no fps drop on auto. The SHS tappet profile is almost identical to the stock one though so I am sure it would also work.
Trimmed sector delay chip
Stock vs SHS tappet

I will point out though that I could not find Genuine SHS V3 tappet plates in Aus so I ended up getting one from Redwolf. The ones I bought in Aus had incorrect markings and did not fit a standard nozzle so be on the lookout for these.
SHS fake vs genuine tappet

Final Parts used:

  • Stock V3 gearbox (radiused)
  • Stock cylinder head
  • Stock nozzle (with o-ring added to extend nozzle)
  • Perun V3 optical mosfet - CQ Blasters
  • SHS 18:1 gears - Azraels
  • SHS delay chip (trimmed) - Azraels
  • Generic 100% rainbow cylinder - Armoured heaven
  • SHS high torque short 480 motor - Azraels
  • SHS V3 tappet plate - Redwolf
  • Modify V2/V3 AR latch - AH Tactical
  • Retroarms 8mm low profile bushes - CEH
  • JM gen 8 nozzle - CEH
  • Aztech piston + piston head - Azraels
  • SHS V3 return spring - Redwolf
  • ASG M95 spring - Ausgel

Completed gearbox

Post modification I am now getting 20rps and an average of 330fps with a nice snappy trigger.

I did also make one external modification which was filling down the mag release to accept the fakelight Rx mags.

Overall I am very happy with the build now it is complete, but it certainly wasn’t the straight forward build I was expecting. In saying that I learnt a heap doing it so it was definitely worthwhile.
Interested to hear if anyone else has experienced these issues too.


Thanks for such a detailed and comprehensive build thread :ok_hand:
This is the sort of good solid information that is needed from members to post up from all the different blasters and mods available across the Hobby/Sport :white_check_mark:
Invaluable for building almost any type of blaster on the market.


Thanks @DocBob. I love reading long posts so I figured it was about time I did one!


Hey, great run down and pics. Just a quick off topic question regarding a V3 gearbox: The only real difference is the shape? As in, all or most internals can be swapped over from a V2? Ultimately I’m wanting to know if an Apache tappetless cylinder head will to fine in a V3. I know they have the option of an extended rubber nozzle to suit a V3, but I can’t seem to find a straight answer elsewhere and this forum is my trusted go-to for solid info. Cheers in advance.

Thanks @Zim777, yeah the main difference is the shape.
The gears, AR latch, piston + piston head, main spring and cylinder are the same for V2 and V3.
The cylinder head is slightly different, being the tube for the nozzle is a bit longer, as there is more tappet travel in a V3 box and some, but not all, V3 cylinder heads have a tab at the top (see below pic).
images (6)

A V2 cylinder head will fit in a V3 box though, just not the other way around if it has the tab on it.
An Apache will run fine in a V3 box, as you mentioned you will just need to adjust the nozzle length and nozzle type to seal properly against the t-piece you are using

I also believe the V3 nozzle extension for the Apache will suit the aps AK t-piece but maybe not the DB one? I don’t have experience with the aps AK’s so I am unsure, but someone else on here might know.
If you have a DB AK the safe bet would be to swap the t-piece to an aps one (see below)

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Right on man, cheers for that. I’ve a JG Aug and thinking of getting a JG Sig while they’re on special at M4A1…I already have an Apache in an APS M4 style and I’m digging the fewer components needed, mind you I had to as I’m using a Scythe split box and they’re designed for tappetless only. The Aug is fairly new and I’ve no experience with a V3 box. Thanks man.


No problem mate. FYI the AUG has a different t-piece to the AK’s so the one I linked will not work. I believe they use a gen 8 style nozzle though so you will likely have to use one on the Apache

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Ok good to know. I havnt quite finnished the APS yet, still nutting out the optimum nozzle length when i can find the time. Learning so much ill be even more confident by time i get to the Aug. Good stuff man, thanks so much.

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Great write up on mods. I’ve been looking at a perun for mine but yet to follow through.
Mine may have been a unicorn, but it remains the only blaster I didn’t have to adjust the shimming to my fussy standards. The only things I changed were the standard o-ring for a brown one which stopped the vacuuming, and a 100% cylinder. now does 390fps all day on semi and full auto.
In hind sight I wish I changed the spring for say an m100 and did the retainer locating mod you did, just to bring the power down (never thought I would say that about a stock spring!).

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Now I may be twisting your arm but If your wanting to take the plunge and get a mosfet this is the best deal I have found.
50% cheaper than everywhere else.

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Oh man… hope they are still that price in a couple weeks, already in trouble with the wife for going a bit nuts with all the sales in the last month! Might be one of those… forgiveness over permission things :wink:

They have been that price since I did my blaster so I reckon they will be

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A quick update, as I recently did some work on one of my DB AKs.
It now has 18:1 SHS gears, an x-force red high torque motor, full cylinder, shs piston and shs nylon piston head with the holes bored out to 3mm.
It was a bitch to shim. I actually wanted 16:1 gears, but the bevel just couldn’t get the right distance horizontally from the pinion as there is stuff all room for shims, and the spur wouldn’t fit with a shim and rubbed the gearbox casing without it. I couldn’t use the stock bearings which were fine, and had to switch to low profile shs bushes. I even used a particular pinion gear as the two other types I keep wouldn’t allow for a decent bevel to pinion mesh.
It was a bastard tbh. Though now with all that and an m100 it gets a neat 370fps consistently! Might even drop to an m90 to get it more field friendly as it is the underfolder variant, and I was hoping to use it indoors as a laugh. Long barrel, and wicked seal and piston just makes it work too well!.
Next DB AK is going to be a shorter version, if I spot one for a good deal!


I just spent half an hour replying to this…… but decided to give up, delete and have a fresh start tomorrow :joy:

Yea I run out of thumb too why most of mine are short and to the point. Then I read what I’ve said and sometimes I don’t even understand it :rofl:

I was half an hour into single letter left thumb work, got lost in my thoughts, turned left at Albuquerque and completely fell down the Rabbit hole :roll_eyes:

Maybe an afternoon of Bundy Cane Cutters Juice, a couple of Jack Daniels and a few Black Ducks (Swan Draught) ain’t a good time to herd up the brain cells into the holding pens! :joy:

You notice how a lot of people go stupid on Bunderburg Rum, get angry want to fight all sorts even just a couple drinks. Yet I can drink a 700ml no worries in a couple hours and none of that shit happens. I imagine you are similar :+1:

Rum does that to me… dunno why. :person_shrugging:

I drink my spirits neat to savour the flavour, and I can go through bourbon, whiskey, brandy, cognac, you name it… no problems. My latest fetish is Sheepdog peanut butter flavoured whiskey. :+1:

If I sit down to a bottle of Coruba, Plantation or Captain Morgan rum ( don’t really groove on Bundaberg, bad Queenslander me :laughing:), after a couple of shots it feels like someone’s taken a blowtorch to my head and I start feeling antsy about stuff.

Maybe it’s because the basis of rum is sugar and not grain like the others. But I have quite a few old mates who you don’t really want to be around when they get on the Bundy. :wink:

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Ooo SHEEP DOG! Now that I down a few bottles lately. That is a nice one, another farmer put me on to that.

All spirits these days I drink neat on the rocks, I’ve gone off coke and such things these days.
Mate brought up some home made bourbon the other week. Damn that was smooth.

When I was young I used to religiously buy a bottle of Jim Beam after work friday night and coke before I’d hit the clubs. Just like it straight these days and minus the clubs :laughing:

Yea with Bundy I dunno what it is but there was the Glenelg Hotel I remember I asked for a Bundy and coke and they said sorry sir we won’t sell that as it starts brawls security can’t handle. No shit. I said oh well surely you got Jack’s hit me :+1: :tumbler_glass:

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