Huben · Custom GK1 Regulated · Cal .25 (6.35mm)

The GK1 is, partially, a downscaled K1, taken from the rifle format to a pistol one. The mechanism block is nearly identical (there are few differences) and many parts are interchangeable. The barrel is a shortened version of the K1 barrel. The most important difference is that the original GK1 is unregulated.

Yes, the GK1 has adjustable power. There is a screw that is accessed through the grip that allows you to increase or decrease the velocity. This controls the time the valve is open, if you turn counterclockwise, the power will increase, if you do it clockwise, it will decrease. As there is no regulator, this is the only adjustable power feature. Being unregulated, the gun’s power will also depend on the total fill pressure. The more pressure, the more power. As you shoot the power tends to decrease, but the descent is gradual. The valve compensates for the drop in total pressure by staying open longer, meaning that the GK1 is more consistent than your average unregulated PCP. However, notice that for this reason, you should always “match” the power regime with the total fill pressure. This means that you can’t let the fill pressure drop down too much (no less than 150-160 BAR), as the gun might experience issues at this point, because the valve stays open too long and might malfunction, dumping all the air. With heavier ammunition, increase the pressure limit where you should refill it (e.g. make it 180 BAR).

Power should always be adjusted gradually, with the assistance of a chronograph so you have a reference of the velocity of the projectiles. The power adjusting screw has no stop, so theoretically, you could unscrew it out – don’t do that. The maximum recommended turns are two (720°). If you absolutely want to reach absurd power levels, then you can make it two and a half turns total, but take care to refill the gun when the fill pressure drops to 220 BAR at least.

Yes, the GK1 can shoot slugs without any problem. Take care to select the correct slug sizes for each caliber. Ideally, slugs should be at least .219 for the .22 and .253/.254 for the .25.

The GK1 originally made by Huben is an unregulated one, however, Wolfiek Group, with the acceptance of the manufacturer, has developed a regulated version. This version includes a regulator inside the air tube and the K1’s filling port with a gauge.

Yes, the power can be adjusted the same as in the unregulated version. The regulated pressure shouldn’t be adjusted, as it is already set at the optimal pressure level for the gun.

The regulated version increases the consistency and efficiency of the pistol, the direct effect of bringing a regulator into the equation. However, notice that the unregulated GK1 is already a quite consistent gun despite being unregulated. The regulator also allows the power of the GK1 to be tuned down further than with the unregulated version. Being unregulated, the GK1 at full pressure can only be lowered so much, while the regulated version can keep the pressure at constant levels, meaning the first shot until the last (when you reach the point you have to refill) will shoot at almost identical power levels.This allows the GK1 V3R, the regulated version, to be set to sub-6 FPE, as the laws in some countries require. The original, GK1 V3 can’t get that far down in its first shots.