This shell is machined just for HPA parts. The price is lower due to the reduced machining time (no need to accommodate AEG parts) and because no spring guide is included.
These Gearbox Shells are fully CNC machined from a block of 7075 T6 Aluminum. This material is very strong and can endure a ton of stress.
Anodized black for corrosion resistance. Comes with screws.
