I was asleep, so missed a lot of opportunity for timely replies. Forgive that.
@shadow187 I have both the generic looking AK and the under folder. The wired stock on the under folder is not very nice on your chin, and the end can be pointy if jammed into your arm pit unexpectedly, compared to the wood stock. Also the wood stock is much thinner, Both are the same length, the folder is also a bit floppy, and there really isn’t much you can do as the mechanism needs a bit of tolerance to click out and in, it is even a thing on real steel. Also when folded it has some slack and makes for a bit of an odd front hand grip. Said folding mechanism also is right where the wires run on the gearbox, so there is very little you can do, and extra care to be taken on re assembling it.
In all, the only benefit of the folder is it can be folded for easier fit in a bag.
As for FPS, out of the box they were both around 360fps on 7v or semi, 11v auto drops to around 320 but that is an average, it is a very inconsistent due to the lack of cylinder volume. Replacing the cylinder with a full one will see it up around 390fps in all modes and batteries.
I had to do nothing else to the full stock version, shimming was good, I did radius it and replace the oring with a brown one as well, for good measure.
My under folder I tried to drop the power by running an m90. They have a double o-ring piston head, and it was too much friction for a light spring and piston and gears had a argument.
My underfolder now has SHS gears, bushes, piston and nylon piston head. Radiused gearbox, full cylinder, and an m100. I did have an m90 and it was comfortably around 320fps, then changed to an m100 and it is up to about 370fps. The longer barrel and full cylinder with a good seal will do that. I have also replaced the motor with a better one that has neo magnets and is a hair faster, did not want to go nuts, just gain some efficiencies.
I short, if you want the power lower, change the piston and head with the spring. Double o-ring piston heads are for airsoft DMRs, and will not end well in gel with lower fps springs.
If you went with a AKSU, the volume is going to be almost bob on, so no cylinder change needed, but you would have more 340-360fps. Longer barrels get a bonus in fps with good seals. Just how it is, the gel has more time to accelerate.
As for FPS vs accuracy, I have always found about 330-340 to be the sweet spot for FPS/accuracy balance, above that you just have to accept that the odd gel is going to spiral way off, but for the most part a burst of 5-6 gels you should get one on target at about 35-40 meters. You really only get an extra 5 meters of range, and if the target sees you shooting at them, they have time to duck behind cover anyway, so it is a bit moot, but is good if you want a lazy day hanging out the back in defensive posture. (I’ve had a few injuries and surgeries in the last year, so I made good use of this).
As for just making it hurt, use white pearls or pink supers. They are not as good gels as ultra hards around, but they are far less fun to take hits from. Softer balls actually sting more. I have theories, and have done enough blind tests with mates to confirm it. Ausgel pink supers always got the “ow, thats the ultras” response. From every one of me and my mates.
Harder is more brittle, breaks up quicker on impact.
It is a V3, so radiusing may not be needed as they are inherently stronger than V2 casings, I just did it as I was in the boxes, and with a needle file it takes a couple minutes so why not. I isn’t something I would charge extra for (some do) as it takes me maybe 3-5 minutes total.
As a final tip, they are in the body, the same as airsoft, so for disassembly, double bell ak airsoft youtube videos are great! And if you are changing to SHS gears, they are a bit of a ball-ache as there is almost no room for shims even with low profile bushings. I had planned to use 16:1 gears, but they simply wouldn’t fit, but 18:1s did so I went with that. both looked to be from differing OEMs, just something to be prepared for if you want to change gears and bushes in them.
Hope some of this helps with you decision, and down the path after purchase