AK Brainstrust,
A friend of mine recently purchased one of these and is looking to pull it apart and check airseals etc.
I did find this thread on V3 upgrades which is very useful, from this and some other research the air seal parts and springs for V2 and V3 gearboxes are generally the interchangeable?
At the moment its getting around 260fps, we’re hoping to get closer to 300
260fps is pretty low for a Double Bell AK, even for the shorter one.
Not sure if they cheaped out on lower power/quality internals on the nylon shell/metal box versions as haven’t had one on the bench yet.
While have heard of their V2 box breaking the front off, haven’t seen it yet on the V3 though I do radius them and recommend it anyway if you are in there.
Parts wise, cylinder, piston, piston head, spring to suit is the easy option for power and reliability to suit.
Volume wise, all Double Bells have the same 70% cylinder. For these and 80% is more what it needs.
Seals, normally there is too much seal with their stupid double o-ring piston heads, or just loads of weight if it is their big thick single o-ring head. Now the metal versions generally did 330-360 fps ootb.
With the double o-ring head, dropping to an m90 to get it closer to 300fps completely stuffs it, will have much lower fps as the spring doesnt overcome the huge amount of friction of the double o-ring piston head.
Their piston also has their own size hole that doesn’t suit most normal heads.
So changing the piston and piston head is recommended. Good quality piston that suits the box, and a nice normal flat faced single o-ring piston head is much better.
Now you have the right volume, and a seal with optimal free movement to just pick the spring that suits you fps requirements.
Nozzles for double bells… you’re screwed and stuck with what they have. Unless you are prepared to do some work!
Watch my double bell PDW part 2 video for details, but where it mounts to the tappet plate and the nozzle throat is similar to LDT, but the tip is similar to a Jin Ming but shorter.
I used an LDT nozzle, and the stock nozzle tip cut down slightly with heatshrink to fill the void between nozzle and tip. Worth noting, heatshrink has worked so far, but I suspect it may cause nozzle tips coming off at some point. Nozzles do get warm with use, so finding something better is ideal, I just haven’t looked into it further as so far it has worked for me.
Can I also suggest, if your friends DB came with a metal magazine, that he purchase a few of these nylon ones from AKGelblaster. The metal ones have a history of snapping the front retaining clip unless very careful. These ones are cross-model compliant and from what I understand, do not share the same issue. Please note the comments on the product link below that some minor filing may be needed to fit the DB.
Sorry @RokSolid I had a reply written but didn’t hit the reply button.
Very helpful post thanks, as always.
He’s ordered some bits and pieces which are slowly arriving so we’ll get into in soon.
For reference he bought the same blaster around 6 months ago and it was doing 300fps, it was also incredibly accurate. Because of that he bought a second as a backup however it was only doing 260fps under the same conditions with the same gels.
Spent about 5 hours on this blaster today and certainly got better at pulling apart V3 gearbox’s, unfortunately that was the only good news as every attempt we made to improve the performance resulted in 140fps.
At first we replaced the cylinder with an SHS %80, an SHS piston and a Tienly piston head. Cylinder head, nozzle and spring remained unchanged. We did air seal tests on the bench with and without the nozzle and they were excellent so we proceeded to do the install, final result was 140fps which had us scratching our head.
Pulled it apart and tested everything again, air seals were good. We did find one weird thing, when testing the air seal with the tappet plate in place, I felt that the tapped plate was slightly lifting the nozzle away from the face of the cylinder head, causing a an air leak when the piston was pushed in for an air seal test.
So essentially, no tappet plate - air seal was excellent.
Tappet plate in place - air seal was around %50 worse off
Tried sanding the tappet plate to get a sharper 90 degree bend where it interfaces with the cylinder head, also tried sanding down the SHS %80 cylinder so it was the exact same length as the factory cylinder (72mm). Also tried again with the factory cylinder but nothing worked. Its probably something simple I’m sure but we couldn’t get to the bottom of it.
New cylinder on the LHS with original cylinder head and nozzle. It this setup the air seal was excellent
When testing the air seal with the tappet plate in place it was about %50
Any idea’s on where to go from here would be appreciated
Get the .357 magnum for a bit, and “lever” alone for awhile??
FFS beemer 
can tell you’ve been waiting to use that one
Double bells are a bit fussy with things at times.
Check the piston moves freely without the cylinder involved… and remove the sector delayer. It just isn’t needed in my experience.
Maybe make sure the barrel spring has enough tension on the tpiece
Ok ta, barrel and t piece we sort of ran out of time to check. Hopefully that’s the golden ticket
Shooting the 357mag down the side of the house is “frowned upon”
I’ve got one of the “traditional” DB AK47’s and it was punching about 380fps, don’t know if the cylinder is ported as it’s a full length barrel and I’ve never had a reason to open it up, I get weird luck with blasters having near perfect seals ootb.
As Rok pointed out, my head goes to it not sealing in the t-piece properly. While it’s together loop through the mag well and see if you can get the timing to have the nozzle completely closed/forward and see if it’s actually closing fully. That
Agree 100%… a hangover from airsoft. 
No ideas sorry but am watching with interest. My DB AK has lost a lot of its FPS and needs a fettling i think. Good luck and look forward to hearing the final fix
The owner of this blaster has two of them, the first puts out 300fps and is a freaking laser beam. This one is 260.
Having two side by side we might be able to identify if there’s an air seal problem with the nozzle or t piece. Be interesting to know what the cause is.
hey i need some help i built a 37rps gearbox with a leviathan v2 optical anyways i am running it on semi and it just keeps jamming i have a apache tappetless cylinder i also bought the aztech adjustable t piece thinking it will fix the jamming issue
None of that has anything to do with the gearbox jamming.
What gears, spring, short stroking do you have?
13:1 shs sector has 3 teeth short stroked m110 spring
Aztech have a specific AK t-piece for Apache and v3 gearboxes. Much difference between that and the adjustable one?
That might be your issue. For that sort of speed you really want an m120, and at least 4 teeth off. Gotta get that piston home really fast before sector comes around!
Does your piston rack have damage on it?
no it doesnt have damage on it so 4 teeth off the sector is what your saying
