【SPARK】Hiei-kai High-Precision Inner Barrel 6.05mm Inner Diameter【EVOLT Exclusive 229mm】(Restock on June 18, 2026)

※Notice※
The Hiei Kai inner barrels for Next-Generation MP5 and EVOLT have been integrated into a single product. Along with this, the JAN code and product code have been changed, so please see the new product page below if you wish to purchase it.
→"[SPARK] Hiei Kai for Next-Generation MP5/EVOLT 229mm Inner Barrel, Inner Diameter 6.05mm"

(Please note that we do not guarantee compatibility with the old Hiei Kai products for Next-Generation MP5 or EVOLT.)

The ultimate inner barrel that achieves the performance SPARK custom engineers demand

It is possible to dramatically improve the accuracy of Tokyo Marui's new EVOLT product.

The "Hiei®" is a high-quality, ultra-precise, domestically produced inner barrel developed by SPARK's concept and the cutting-edge metal processing technology of artisans from "da Vinci," the manufacturer behind the custom barrel series "Guren / Raizen." From there, further improvements were made to various parts, resulting in the birth of the "Hiei® Kai," the ultimate refined inner barrel.

The base material used is the highest quality domestically produced stainless steel manufactured by cold forging, and it is meticulously crafted by Japanese artisans using a domestically produced high-precision CNC machine.

To ensure stable HOP application, the shape and polishing of the HOP window are thoroughly optimized, and the barrel's end features a 20 mm super-long taper designed to envelop the BB bullet in an air layer!
Combined with the 6.05 mm tight diameter, this results in improved muzzle velocity, accuracy, and range.

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

【Features of Hiei® Kai】

Ultra-Polished HOP Window

• For a stable trajectory, stable "hop-up application" is crucial.
• Artisans meticulously polish the inner wall, including the area around the HOP window, to eliminate uncertain factors affecting BB bullets.
• By applying highly difficult "round cutting" to the HOP window, the HOP packing moves smoothly, maximizing the performance of the HOP packing.

20 mm Ultra-Long Taper

• Extremely hard cold-forged stainless steel is very difficult to process due to its hardness, requiring a high-precision CNC machine, the selection of cutting tools by skilled artisans, and precise programming for processing. The unconventional 20 mm ultra-long taper suppresses rapid changes in resistance and increases in turbulence coefficient around the barrel exit, eliminating adverse effects on accuracy.
• This brings out the gun's inherent accuracy to its fullest potential.

Pride in being Made in Japan

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