its a gas piston system Mid length, Short Stroke Piston Operated

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Hi Wilfredo, The EVO is a Mid length Gas System , Short Stroke Piston Operated SPECS - • Mil-Spec Forged 7075-T6 Lower Receiver, Type III Class II Hard-coat anodized finish, beveled magwell, machined chevrons in front strap
• Mil-Spec Forged7075-T6 M-4 Upper Receiver, Type III Class II Hard-coat anodized finish, M4 feed ramps, 1913 Picatinny rail flat top with dry lube internal finish and laser engraved T-markings
• 14.5" Medium Contour 4150 CM Melonited Barrel 1:12 twist
• Chambered 300BLK
• Magpul MOE Grip
• Magpul MOE Trigger Guard
• Magpul 6-Position Stock
• VDI Jet Comp
• VDI LifeCoat Firing Pin
• 30 round Magpul PMAG Magazine
• Samson free float light weight modular rail system

This rifle's Gas System is: Mid length, Short Stroke Piston Operated Wilfredo.