Heng long 1/16 tank airsoft upgrade for shot unit

I wanted a bit more oompf from the 8.8 in my rc tiger AND more reliable feeding without compromising longevity of the plastic gearbox, so I designed this part to use my leftover barrel and hop up bucking from a airsoft "AEP" mp7. The stock barrel length in the tank is surpassing the capacity of air in the cylinder, and combining that with crappy surface finish, large diameter and 2 drilled holes in the barrel the resulting efficiency and output is pretty weak. The mp7 AEP barrel length is perfect for an approx. 1.1/1 cylinder/barrel volume ratio, so the BB exits the barrel just as the piston strikes its end, theoretical 100% efficiency. The stock air seal is also non-reliable at best, with this it should be 100% each shot.

You need to get a hold of mp7 barrel and airsoft AEP bucking (smaller than AEG buckings) in addition to this part. You might wanna source a 6.01 precision barrel for best possible output, but I used a brass 6.08 barrell that I polished internally. Also, depending on brand of hop bucking you might need to grind the bb opening so the bb can pass relatively easy through, else the nozzle might struggle to feed bbs through resulting in major power loss. Dont overdo this part though, there should be some resistance for the BB to pass to avoid double feeds. You may also need to machine out some plastic from your outer barrel or do other mods in order to mount the new barrel. So far I have only tested mine in a Tiger 1, and I had to do some minor machinig as the brass barrel diameter was larger than the stock barrel.

I also included a hole you can tap with a 3mm tap or force a screw into to attach a set screw for hop up adjusting. This part requires som DIY'ing to other parts depending on how you want it, but its easy enough. I drilled a small hole on top of the turret that just fit an allen key for adjusting from outside the tank.

The ring is there to sort of lock the barrel and hop bucking in place. It may be a loose or tight fit on the barrel, depending on outer barrel diameter. You can adjust the scale before printing if its either of those things. Some minor sanding may also be required in order for it to fit inside the new barrel housing. Thread it on first with the thinner side facing the rear of the barrel, then bucking, insert the barrel into the new barrel housing with the hop "lip"/barrel groove facing up and rest the barrel ring tight against the hop unit, now place it inside your shot unit gearbox shell and reassemble it.

From the looks of it, this part should be able to drop into most shot units for these tanks with minor to none trimming internally of the shot gearbox shell. You need to disassemble the shot unit, but that is pretty simple.PLA prints 1/1 and should be a perfect fit.

With this and a 6.08mm MP7 AEP barrel installed I went from 15m/s to 30m/s using 012gr bb's, and 8 to 16m/s using 0.2gr bb's. With a 6.01 it might gain a few more m/s, and a fresh spring in the bullet gearbox might even add more. Accuracy can be adjusted to your bb weight if you choose to utilize the screw hole.