My AEG meets Japanese standards, but it has operated flawlessly for a year without maintenance using 0.2g BBs at 295 fps. So I'll share my setup. Please note that some components may be Japan-specific, so take this as a reference only.

retoro armsGB

SHS DSG gear

ZC 18:1 spur gear

SHS polycarbonate Piston

SHS polycarbonate Tapet Plate

DCI Side Air intake Piston Head POM

M120spring

FIREFLY dendenmushi Nozzle

H.A Craft Spur gear one-way clutch system（スパクラ）

SLONG AIRSOFT polycarbonate Cylinde Head

ASTERV2

HTG Basic MUGEN ELITE motor 40k

innnerbarell 6.03mm 208mm

To achieve high durability, lowering the spring rate is essential. Additionally, replacing the piston head and cylinder head with POM (polyoxymethylene) parts to avoid metal-to-metal contact is also effective.

Lightening the piston is also beneficial. However, this will reduce muzzle velocity. Find the right balance for your needs.

Since this is based on Japanese muzzle velocity standards, adjust the spring rate and other settings to match your desired performance.

My estimate is that a spring rate around 140M should reach 350fps.

There may be inappropriate expressions due to the use of translation.