Update 2024-10-24: Due to many requests there are now upper receivers with a Picatinny rail (STANAG 4694) available. I did not print them myself. Please post a make or at least provide some feedback because you wanted this ;)

This is an attempt for a slim, minimalistic and light weight Upper Receiver with Hand Guard while still being compatible to standard components. It aims at Speedsoft players and should make the hobby more accessable.
Disclaimer (because people are stupid): I am not responsible for any damage you deal to your airsoft replica by using or attaching this design. Please keep in mind that this is not a true "plug'n play" part. It demands some basic technician skills and some understanding of how airsoft guns work.

Upper Receiver

This design can be used with any build that utilizes the Gear Box Shell. Either HPA or (S)AEG. You have to cut the upper „fin“ off.
Removed all unnecessary stuff like Forward Assist, Dust Cover, Charging Handle, etc. The Hopup Chamber Rotary Dial can be operated ambidextrously and even during the game. The seat for the Hopup Chamber (which is usually part of the Outer Barrel) is now integrated in the Upper Receiver. Due to the tight fitment it may increase your groupings (less wobble, sliding forth and back, etc.) but requires extra work or at least some attention during assembling.
Thread for the Barrel Nut is „EU“ (M32 x 1,5mm). This allows you to attach most aftermarket Hand Guards, if you like. The Inner Barrel needs a "stabilization thing" in case of that.
Removing the supports from the seat of the Hopup Chamber is really not a nice job when printed in PETG. Just be patient and bring suitable tools.

Variations

Upper and Lower Receivers differ from manufacturer to manufacturer. Most differences can be spotted at the front take down pin. The bodies also vary a bit at the back where the Upper locks in.
Specna Arms - The Upper Receiver was originally designed for Specna Arms Edge Lower Receivers. So this one received the most love and adjustment.
G&G - Being lucky, I got my hands for a short period of time on a G&G SSG1 which resulted in a dedicated version for G&G Combat Machine Lower Receivers. It was a rushed design adaption, so please excuse possible misfits (never printed the final version). Since most Speedsoft builds are based on G&G lowers, it may be useful for some of you out there.
Cyma / Generic – This is a spin-off from the original Specna Arms version. The block at the front for the take down pin is 2mm smaller (so you do not need to file it down on your own). To fit it on a Cyma you have to file the hole a bit in backwards direction. Other manufacturers may need different modification.

Tested Hopup Chambers

The springs on the Inner Barrel are meant to be not used anymore. If the Hopup Chamber comes with the small spring on top / above the barrel, you may use it (optional).

• SHS CNC V2 II (shooting lasers)
• Cyma Default Rotary Chamber (shooting lasers)
• Silent Industries AEG Alpha (requires some O-Rings, as intended)
• MAXX M4P Pro (sprayed)
• MAXX M4A Pro (sprayed, feeding tube maybe to short or my mag catch was worn out)

Hand Guard

Designed for common Inner Barrel length of 128, 155, 205, 229 and 247mm. For my own needs I added a 186mm version. The Inner Barrel will stick out ~5mm and allows you to push out the Hopup Chamber without unscrewing the Hand Guard. Those ~5mm are substracted at the file names. Since there is no traditional Outer Barrel the Hand Guard adds stabilization to the Inner Barrel at the front. This results in a "two point fixation" which is considered the best (because it does not bend the barrel).
The muzzle area comes with a 14mm CCW thread and an inner diameter of 29mm wide. So tracers like the Acetech Brigther C will fit. The tracer allows up to 10mm excess length. The Hand Guard acts as apron for the tracer.
The Buffer Tube thread is EU (M32 x 1,5mm). If you want to add Picatinny rails or something: just drill through, then attach it with screws and nuts. There is enough space inside :)

Misc

The stabilization of the Inner Barrel and Hopup Chamber was unintentional but a welcome surprise.
The SketchUp file for the Hand Guard is attached. Just in case you want to use another Inner Barrel length or add a Picytinny rail for your action cam or change something else, please check the license and act accordingly.
Some pictures are from the time when the design was still in development.

Dedication

This design is dedicated to my favourite CFR and former best friend. Reliable, honest, quick thinking and straight. You will be missed.