Time for an update... Got a lot done today. But first, M60 porn lol.
The new nozzle (Modify nozzle for VFC SCAR-H w/ integral o-ring) is about 1/4" too long, so I sanded it down with a file, then sanded a 45 degree angle to the ends. Finished it off with some 1500 grit sandpaper to smooth out all the edges from the burrs.
And here is the gearbox with all the new parts, before new grease. The new nozzle fully solved my air seal issues as you will see...
I immidiately tested with the original spring, but with a new piston/piston head, one piece cylinder/cylinder head, nozzle, motor, and wiring. 0.2g Elite Force BB's were used with a 9.9V LiFe battery. The results speak for themselves, at 18 rps (hit 19.4 max) and 466 FPS max recorded, lowest was 454, hitting 460 FPS about 80% of the time... This is ~30 FPS higher than the gun recorded originally with A&K parts. However I have about as perfect an air seal as I can expect to have with an airsoft gun and parts that will wear better and last longer. Which is important when you'll burn between 5000 and 10 000 rounds or more a game.
Next I used a Promethius M120 spring (known to behave more like an M130). It chronoed at 460 consistently, indicating that the factory A&K spring is likely an M130 spring. next I used a Modify M120, hitting 440 FPS, next a Lonex M110 spring, hitting 435 consistently. I did not have an M100 spring so I cut about an inch off the M110, and refinished the cut edge so it would stay secured to the spring guide and not slip off. It chronoed as below, 395 +/- 3 FPS. The reduced ROF could be due to the battery losing power, it's a 2100 MAH battery but I've yet to charge it and it's seen likely about 3-4 thousand rounds lol.
Anyway 400 ish FPS is exactly where I want it. I don't want to max out the power (420 FPS is my local fields rules) and this gives me some flexibility if the field chrono is reading high, and also it's a support weapon - less stress on the gearbox and I'll likely be hosing people from time to time if I suppress an area aggressively.
