The New Gen 8 M4A1 is usually a top-of-the-line gel blaster, that contains casted metal gears and metal piston, a metal interior barrel and also a higher toughness gearbox in comparison to the aged version of Gen 8. https://kkgelblaster.com/collections/best-sale/products/kkgelblaster-fjs-m4a1-cqbr-gel-blaster