【SPARK】Hiei-kai High Precision Inner Barrel 6.05mm Inner Diameter [For GHK CO2 AR Series]

GHK CO2 Compatible Hiei Kai Inner Barrel
The ultimate inner barrel that meets the performance standards of SPARK custom engineers

The Hiei®, a high-quality, ultra-precision inner barrel proudly made in Japan, was developed with SPARK's concept and the cutting-edge metal processing technology of da Vinci, the manufacturer behind the "Guren / Raizen" series of custom barrels. Now, with further improvements to various parts, the ultimate and most refined inner barrel, the Hiei® Kai, has been born.

It is crafted from the highest-grade domestically produced SUS304 stainless steel, manufactured through cold forging, and precisely machined using a high-precision CNC machine, also made in Japan.

To ensure stable HOP application, meticulous attention has been paid to the shape and polishing of the HOP window, significantly reducing wear below the HOP window and preventing dirt from adhering to the inner wall when applying HOP.
Combined with its tight 6.05mm diameter, it boosts muzzle velocity, improves accuracy, and increases range.

At the muzzle end of the barrel, anunconventional 20mm long taper reduces exit loss in fluid dynamics, enhancing both accuracy and range.

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

■For GHK GBBR V2/V3
Complies with the standards of the GHK CO2 GBBR V2/V3 series.
As there is no clear standard, please understand that even with the same specifications, some overseas products may not be compatible.

▶Compatible Models (as of April 2026)

• GHK CO2 GBBR V2 (2022 onwards)

• GHK CO2 GBBR V3

※The above is an example of confirmed products. If the specifications are the same, it may be usable with main units not listed.

■Overall Length
・175mm
Optimal for DDM4 PDW

・210mm

・250mm
Optimal for 10.5-inch barrels. For 14.5-inch class barrels, an separately sold spacer is essential.
Mk18 → 250mm can be used as is
M4A1 14.5inch → 250mm + separately sold GHK barrel spacer required

【Features of Hiei® Kai】

Ultra-Polished HOP Window

• For a stable trajectory, a stable "hop-up application" is crucial.
• Craftsmen meticulously polish the inner wall, including the area around the HOP window, to eliminate uncertain factors affecting BBs.
• The HOP window undergoes highly difficult "round cutting processing," which smooths the movement of the HOP rubber and maximizes its performance.

20mm Ultra-Long Taper

• Extremely hard cold-forged stainless steel is very difficult to process due to its hardness, requiring a high-precision CNC machine and skilled craftsmen for selecting cutting tools and precise programming for processing. The unconventional 20mm ultra-long taper suppresses sudden changes in resistance and increased turbulence coefficients around the barrel exit, eliminating adverse effects on accuracy.
• This brings out the gun's inherent accuracy to its utmost limit.

Pride of Made in Japan

• The intricate 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.
• The "Hiei® Kai" is a MADE IN JAPAN product that Japan proudly offers to the world.

※Regarding Legal Power Limits
Incorporating an inner barrel may cause the firearm to exceed legal power limits. Always use a chronograph to ensure the power remains within legal limits. We are not responsible for any violations of laws, ordinances, or field regulations resulting from the installation of this product.

Gas blowback guns should be adjusted to remain within legal power limits when the magazine is at 35°C.
※This is based on the legal requirement for measurements to be taken indoors at temperatures between 25°C and 35°C.
※Overheating the magazine can cause it to rupture, potentially leading to injuries.