[AIRSOFT97] Hi-Ei Kai for Next Gen MP5/EVOLT 229mm Inner Barrel, 6.05mm Bore (Restocking August 31, 2026)

Regarding this product:
The Hiei Kai inner barrel for next-gen MP5 and EVOLT models have been integrated into this single product.
(Please note that we do not guarantee compatibility with the old Hiei Kai models for next-gen MP5 or EVOLT.)

The ultimate inner barrel, achieving performance that satisfies SPARK custom engineers.

Developed with SPARK's concept and the cutting-edge metalworking technology of craftsmen from 'da Vinci', the manufacturer behind the custom barrel 'Guren / Raizen' series, 'Hiei®' is a purely domestic, high-quality, ultra-precision inner barrel. Further improvements have been made to various parts, resulting in the birth of the 'Hiei® Kai', the ultimate, most refined inner barrel.

It uses the highest quality pure domestic SUS304 stainless steel, manufactured by cold forging, and produced with precision processing by pure domestic high-precision CNC machines.

To achieve stable HOP engagement, great care has been taken in the shape and polishing of the HOP window, significantly reducing wear below the HOP window and dirt adhesion to the inner wall that occur when applying HOP.

An extraordinary 20mm long taper at the end of the barrel reduces exit losses in fluid dynamics, improving accuracy and range.

*The airsoft gun inner barrel "Hiei" is a registered trademark of SPARK Co., Ltd.

■ About Next-Gen MP5 / EVOLT Series

Compliant with Tokyo Marui Next-Gen Electric Gun MP5 series and Tokyo Marui EVOLT series standards.
Please understand that since there are no clear specifications defined, even if foreign products use the same standards, they may not be compatible.

【Features of Hiei® Kai】

Ultra-Polished HOP Window

• Stable trajectory relies on stable 'hop-up engagement'.
• Craftsmen meticulously polish the inner wall, including the area around the HOP window, to eliminate unpredictable elements affecting the BB bullet.
• The HOP window undergoes highly difficult 'round cutting' processing, allowing the HOP bucking to move smoothly and maximize its performance.

20mm Ultra-Long Taper

• Extremely hard cold-forged stainless steel is very difficult to process due to its hardness, requiring high-precision CNC machines, the selection of cutting tools by skilled craftsmen, and precise programming for processing. The extraordinary 20mm ultra-long taper suppresses sudden changes in resistance around the barrel exit and increases in turbulent flow coefficient, eliminating negative effects on accuracy.
• This maximizes the inherent accuracy of the gun.

Pride in Japanese Craftsmanship

• The precise round cutting of the HOP window, the polishing of the barrel's inner surface, and the long taper processing on the muzzle side are easy to describe in words, but creating an ultra-precision inner barrel from difficult-to-process cold-forged stainless steel requires high technical skill.
• 'Hiei® Kai' is MADE IN JAPAN, a source of global pride for Japan.