FPS doesn’t seem right?

[robbiec97]

Hi all, ive got a Specna Arms SA-F01 running the following..

SA 13:1 Steel Gears
SA CNC Aluminium Ported Piston
SA CNC Ball Bearing Piston Head
Prometheus Aero Cylinder Head
SA Aluminium Nozzle
SA High Torque Motor
SA 6.02mm Tightbore Inner Barrel
Prometheus Purple Bucking
Gate PicoSSR 3 Mosfet
Nuprol 11.1v 1300mah 20c Li-Po
FPS M110 Spring

Currently getting approx 320 FPS, does this seem right? I have been over everything with a fine tooth comb, and can not find a thing out of place. Seems to be perfectly air tight in all places, passes the ‘paper test’.

Im fairly new to Airsoft tech’ing, so please go easy if you believe some of the parts should not have been put in, but stock was only giving me 250 FPS, so I had to do something? Also very interested in all this, so any help or suggestions would be fantastic!

Thank you in advance!

 

[Cannonfodder]

Possibly a silly question but is that fps with .2g bbs?

 

[robbiec97]

Yes it is, sorry, should have added that!

 

[Leo Greer]

That's not crazy. It's very possible that you have a good seal and the FPS is just that low. But, there are some things that could be done assuming you do indeed have a bad air seal.

First off, I should note that most airsoft springs on the aftermarket are badly made and badly labeled. This leads to huge inconsistency just based on which individual spring you got. Unless it's a high quality maker like PDI or Guarder, you could very well just have a weak spring. Also, airsoft spring rating systems are often completely arbitrary--old makers had systems for how they rated springs (PDI % system is % of original Tokyo Marui spring power), but newer brands/makers typically have no good rating method. You can see this by the huge FPS range that will be listed with springs. For example, I once used an SHS "M120" that gave me 2J, which is absolutely ridiculous. On the other hand, springs by quality aftermarket makers, and even quality stock makers will all be consistent. As an example, I tested four separate Arcturus springs and all of them gave near identical, very consistent, readings.

Now, here's where you could be losing air, assuming you actually do have an air leak:

The main place you could be losing air is your nozzle to hop packing seal, which is easily the hardest to achieve. The Prommy purple is a "legacy" hop rubber, meaning the spec is built for legacy hop units, barrels, and nozzles. To test, you could pick up a cheap "modern" rubber, such as the Krytac Orange and test it out.

What's the FPS consistency? Meaning, how large is the variation between shots. Bad consistency can be an indicator of poor seal.

If the FPS consistency is bad, you might try your stock nozzle. Nozzles are one of the most finicky things about airsoft, and sometimes makers will even sell nozzles of the wrong length for certain models that will work, but may not provide optimum seal and performance. It's worth noting that most stock air nozzles are just fine from the get go--there's not a big call to replace them unless yours specifically had something wrong with it.

Assuming everything's put together well, that build should do you just fine, but it is worth mentioning that most of those parts aren't upgrades over stock parts, and some are actually downgrades, being functionally worse than stock. For example, stock cylinders are pretty much fine across the board (no need to replace 95% of the time), and aluminum pistons are just terrible.

As a final test, do the FPS readings change any between full auto and semi? That build strikes me as being very susceptible to PME, which is where the drivetrain spins faster than the piston can return and causes premature contact between the gear teeth and the piston rack.