I bought a broken SU-16 as a project rifle, I'm an engineering student so I want to try improving the design.
From a technical point of view, the design of the bolt and piston system is clever, it's because of that design that a polymer upper can even be used. I like the design of the folding stock, and I like the look and feel of the standard stock which can hold AR mags. However, the design of the receiver in of itself is very poor for polymer application. It almost looks like they designed it with the mindset of something you'd have CNC'd in metal. Another problem with the use of the polymer upper is that polymer naturally flexes, even with reinforcement fibers or other additives, it will always flex to some degree. What this does is it can slightly mess-up the alignment of the bolt and the chamber, I've observed slight misalignment damage to both the chamber and bolt of my gun.
Though not catastrophic, it shows me that they really didn't fully consider the properties of the material before going into production. It should be noted that unless you're well versed with specific material properties, it is often hard to understand what will happen until you actually put it into action, and even then things can go wrong when you bring that product into mass production.
Perfection isn't possible, but safety and operational tolerances should be maintained to such a degree that errors in the end product won't cause a catastrophic failure, of course this will always increase the cost of production, but you can't build a good reputation without those vital elements.
The spring in the piston system is also cheap and in my opinion unsuitable to the application, simplicity is essential to a reliable system, however in this case I believe something more suitable should have been designed for prolonged life and reliable operation of the rifle, mind you the spring is probably only 10-20 dollars to replace. But this spring is actually the key to the whole rifle, if that spring fails, the gun WILL break, as is what happened to the rifle I received, and is what I imagined happened to many other early versions of the gun which broke.
They fixed the issue by thickening the rear of the upper, but I think the inherent flaws in the design should've been addressed instead of this band aid fix, even if the rifle would be more costly to make, it'd be worth addressing the problems with the barrel mounting system and the silly upper design.
Talking about the barrel, it's quite sad that they'd make it a threaded barrel only to have it essentially irremovable. I've already thought of dozens of ways they could've changed the design to permit a changeable barrel and fix the inherent flaws, without gouging the production cost of the rifle unreasonably.
That being said, I hope redesign the upper receiver to fix these issues, and share the information with the forum open source style. I currently plan to make both a 3D printed upper receiver, to prove that polymer can indeed be used successfully with proper design, and a CNC'd/stamped steel version to showcase how well it could perform with more appropriate materials, all the while maintaining a suitably low cost as per the nature of the rifle.
I will share .stl files, G-code, and build plans once the project is completed. I plan to begin the project in December during the break, and continue it throughout the year till completion.
To summarize, the rifle is a mix of good and bad, it could be more, but you get exactly what you pay for. I believe a rifle like this, given its limitations and flaws, is suitably priced around 500-600 dollars; which is about the price of the gun down in the US, the higher price we pay is obviously entirely due to our limited market and government influence.
I hope this semi-technical review helps potential consumers.
