Huben Huben GK1 .22: A Beginner's Journey to a DIY Mini Carbine

[Navig]

So: Out of the box with JSB 18.13gr pellets.

Here is the FX chronograph data dump:

Notes
Bullet: Diabolo
Weight: 18.13 gr

Shot count: 16
Low: 361
Hi: 375
Avg: 367
STD Dev: 3
Spread: 14

2024-01-11 20:57:49,370,FPS,5.5,FT Lbs,
2024-01-11 20:57:57,375,FPS,5.7,FT Lbs,
2024-01-11 20:58:09,371,FPS,5.5,FT Lbs,
2024-01-11 20:58:11,369,FPS,5.5,FT Lbs,
2024-01-11 20:59:07,366,FPS,5.4,FT Lbs,
2024-01-11 21:09:40,366,FPS,5.4,FT Lbs,
2024-01-11 21:09:44,367,FPS,5.4,FT Lbs,
2024-01-11 21:11:43,370,FPS,5.5,FT Lbs,
2024-01-11 21:12:18,367,FPS,5.4,FT Lbs,
2024-01-11 21:12:22,369,FPS,5.5,FT Lbs,
2024-01-11 21:12:56,367,FPS,5.4,FT Lbs,
2024-01-11 21:13:02,364,FPS,5.3,FT Lbs,
2024-01-11 21:13:15,366,FPS,5.4,FT Lbs,
2024-01-11 21:13:40,364,FPS,5.3,FT Lbs,
2024-01-11 21:13:47,363,FPS,5.3,FT Lbs,
2024-01-11 21:14:00,361,FPS,5.2,FT Lbs,

Charts like this are typically a list of the shot# in order, the speed the pellet traveled (feet per second or fps) and the energy of pellet at the chronograph measure point (FPE or foot-pounds of energy). The energy is calculated from the weight and speed of the pellet, ie ye old formula E=1/2mv^2. There are online calculators to do the math and work out the units for you.

Unsurprisingly, the pistol seems to be tuned to 6 FPE. which I think is a UK legal requirement. We will adjust that later.

 

[scottblair]

I use a canted red dot on my rifle. It works great for 30yds and under. Eliminates the problem you've described.
On my pistols, I also use a red dot and have not really noticed much difference in poi between 5-20 yds.
Do you think this is attributed to the height over bore being low, or just the nature of red dots vs scopes?

Red dots work the same as scopes in regards to any hold over. But yes, they can sit much closer to the bore, which means less loopy hold over required.
HTH.
Have fun!

 

[ChRiSiS]

So: Out of the box with JSB 18.13gr pellets.

Here is the FX chronograph data dump:

Notes
Bullet: Diabolo
Weight: 18.13 gr

Shot count: 16
Low: 361
Hi: 375
Avg: 367
STD Dev: 3
Spread: 14

2024-01-11 20:57:49,370,FPS,5.5,FT Lbs,
2024-01-11 20:57:57,375,FPS,5.7,FT Lbs,
2024-01-11 20:58:09,371,FPS,5.5,FT Lbs,
2024-01-11 20:58:11,369,FPS,5.5,FT Lbs,
2024-01-11 20:59:07,366,FPS,5.4,FT Lbs,
2024-01-11 21:09:40,366,FPS,5.4,FT Lbs,
2024-01-11 21:09:44,367,FPS,5.4,FT Lbs,
2024-01-11 21:11:43,370,FPS,5.5,FT Lbs,
2024-01-11 21:12:18,367,FPS,5.4,FT Lbs,
2024-01-11 21:12:22,369,FPS,5.5,FT Lbs,
2024-01-11 21:12:56,367,FPS,5.4,FT Lbs,
2024-01-11 21:13:02,364,FPS,5.3,FT Lbs,
2024-01-11 21:13:15,366,FPS,5.4,FT Lbs,
2024-01-11 21:13:40,364,FPS,5.3,FT Lbs,
2024-01-11 21:13:47,363,FPS,5.3,FT Lbs,
2024-01-11 21:14:00,361,FPS,5.2,FT Lbs,

Charts like this are typically a list of the shot# in order, the speed the pellet traveled (feet per second or fps) and the energy of pellet at the chronograph measure point (FPE or foot-pounds of energy). The energy is calculated from the weight and speed of the pellet, ie ye old formula E=1/2mv^2. There are online calculators to do the math and work out the units for you.

Unsurprisingly, the pistol seems to be tuned to 6 FPE. which I think is a UK legal requirement. We will adjust that later.

Interestingly my.22 GK1 arrived from Kraz Cool airguns set to just over 600 FPS with FX 16 grain pellets. This was defined as Low Power in the docs he sent with the pistol, but its a lot higher than yours above.

Shot count: 12

Low: 598 FPS
Hi: 610 FPS
Avg: 603 FPS
Spread: 12 FPS
STD Dev: 3.6 FPS

15-Feb-2024 18:06:03,598,FPS,12.7,FT Lbs,
15-Feb-2024 18:06:08,610,FPS,13.2,FT Lbs,
15-Feb-2024 18:06:12,608,FPS,13.1,FT Lbs,
15-Feb-2024 18:07:16,601,FPS,12.8,FT Lbs,
15-Feb-2024 18:07:17,605,FPS,13.0,FT Lbs,
15-Feb-2024 18:07:20,605,FPS,13.0,FT Lbs,
15-Feb-2024 18:07:34,598,FPS,12.7,FT Lbs,
15-Feb-2024 18:07:36,601,FPS,12.8,FT Lbs,
15-Feb-2024 18:07:37,601,FPS,12.8,FT Lbs,
15-Feb-2024 18:07:38,601,FPS,12.8,FT Lbs,
15-Feb-2024 18:07:40,605,FPS,13.0,FT Lbs,
15-Feb-2024 18:07:41,603,FPS,12.9,FT Lbs,

 

[sactargetshooter]

Sactaregetshooter--Sounds like you are referring to what I researched as "Height over bore". I ran in to this phenomenon because it rained nearly constantly in NorCal in January and February. So I had to do a lot initial shooting in my shop, which gives me a range of about 30 feet. When I moved outside to a longer distance, my point-of-impact was above my crosshair, which might be counterintuitive--usually the longer away the target, you want to aim higher to account for pellet drop. Instead, I had to aim lower to hit the farther target. As you said, in close close range, the height of the optic above the bore of the barrel, comes in to play. So you have to account for it, or minimize it by mounting the optics as low as possible. More on that when I get to mounting optics and designing my optics rail.

In summary you have 3 ranges. In ultra short range, the height of you optic causes the point of impact to be lower than you might expect. Normal range is where you typically will have your optics adjusted. Then ultra far range, your point of impact will once again fall below your crosshair as the pellet start dropping. The difference between ultra short and normal range can be minimized by keeping the optic as close to the level of the barrel as possible.

I am also in NorCal, @Navig (Sac as in Sacramento). You are absolutely correct about scope height/height-over-bore.

For a high performance (muzzle velocity) pistol/micro-carbine like the GK1, part of the appeal is the long range capability. There is no way to avoid BDC because of the relatively low muzzle velocity (compared to PB). To maintain the flexibility to shoot as a pistol and as a microcarbine with shoulder support, I think a red dot is the way to go. There are very few red dots that have elevation turrets.

The first one is the UltraDot. The problem is that the elevation adjustment is in units of MOA. One MOA is 1" at 100 yards. The second one is the Leupold RDS where elevation adjustment is in 1/4 MOA. The UltraDot has a 2 MOA dot, while the Leupold has a 1 MOA dot.

I would zero the gun for PBR, then adjust for drop for long range shots. From what I have seen on YouTube, the GK1 is one of the guns that can reasonable groups at 100 yard!

 

[longdog]

I am also in NorCal, @Navig (Sac as in Sacramento). You are absolutely correct about scope height/height-over-bore.

For a high performance (muzzle velocity) pistol/micro-carbine like the GK1, part of the appeal is the long range capability. There is no way to avoid BDC because of the relatively low muzzle velocity (compared to PB). To maintain the flexibility to shoot as a pistol and as a microcarbine with shoulder support, I think a red dot is the way to go. There are very few red dots that have elevation turrets.

The first one is the UltraDot. The problem is that the elevation adjustment is in units of MOA. One MOA is 1" at 100 yards. The second one is the Leupold RDS where elevation adjustment is in 1/4 MOA. The UltraDot has a 2 MOA dot, while the Leupold has a 1 MOA dot.

I would zero the gun for PBR, then adjust for drop for long range shots. From what I have seen on YouTube, the GK1 is one of the guns that can reasonable groups at 100 yard!

I actually bought another barrel shroud for my .25cal.
I have a Leupold RDS on one shroud and a Vector 3X12 compact scope on the other.
I shoot the RDS setup most of the time because the Vortex setup gets quite boring out to 50 yards.
I can switch between the two shroud/sights in less than a minute with each holding it's zero.
Absolutely love this gun!

 

[sactargetshooter]

I actually bought another barrel shroud for my .25cal.
I have a Leupold RDS on one shroud and a Vector 3X12 compact scope on the other.
I shoot the RDS setup most of the time because the Vortex setup gets quite boring out to 50 yards.
I can switch between the two shroud/sights in less than a minute with each holding it's zero.
Absolutely love this gun!
View attachment 441203

Way cool! I am surprised that switching between shrouds does not require re-zeroing, that is some precision machining there!

The 1 MOA dot plus 1/4 MOA adjustment of the RDS should allow you to "reach out" quite a bit. How did you purchase the additional shroud if you don't mind me asking?

 

[longdog]

Way cool! I am surprised that switching between shrouds does not require re-zeroing, that is some precision machining there!

The 1 MOA dot plus 1/4 MOA adjustment of the RDS should allow you to "reach out" quite a bit. How did you purchase the additional shroud if you don't mind me asking?

I got the extra shroud from Kelly at KrazKool.
When swapping out the shrouds I've learned that if I let them "seat" themselves(muzzzle up) and then tighten them with the same torque each time they do not require re-zeroing.

 

[Navig]

Wow, thanks guys, so much information and cool stuff to digest! As I have mentioned, I will get back to optics in a few posts.

@sactargetshooter , I'm in Chico baby! Lucky enough to be on my own 5 acres. The bloom from the other day, altho the windstorms of yesterday and today have pretty much ended the bloom.

We ALL HUNT squirrels. Lucky enough that I am in a community where I don't have to moderate my airguns for the sake of my neighbors.

Which does segue into my next post...

 

[Navig]

Ok, Check! The pistol works proper out of the box!

What was my next step? Custom speed loader? Optics mount? Optics testing? Ammunition testing?

Nooo! I think everyone would agree that the first thing to do to this pistol is to get a moderator on it. Because it is loud. All of my previous air rifles had some sort of built in sound suppression. Not the GK1. Even at 6 FPE (lethal only for small birds close by), this pistol is loud. And there is going to be a lot of shooting this pistol, for sure.

Stick a 7mm allen key (who has a 7mm allen key handy--nobody. 1/4” worked fine for me) and unscrew the Barrel shroud end cap.

Screw on a 1/2x20 thread adapter from Ares (someone else may have the answer about whether Huben is now including one with their pistols). If they are not, buy one. I highly recommend a moderator of any sort to protect your ears.

And, screw on my Hugget Snipe Moderator:

A couple of notes on the first few shots. With a moderator, it seems much quieter and less violent than my other hammer based air rifles. It was and still is lovely. Yes, get a moderator, any moderator, on there because it is so likely you will be going through tin after tin of pellets. Pretty much every tinkering session I had with this pistol began with full magazine unload and a smile, and ended with a full magazine unload and a smile.

There are endless moderator recommendations and threads. Taming the Bark is a tremendous thread. Obviously the Hugget is a high class moderator, and so is no way holding this setup back from being an awesome minicarbine. But for sure I will be circling back and printing my own moderators in the future!

 

[Navig]

Now that I've got a vetted pistol that I was happy to shoot endlessly, my next step was to quickly rough tune the power to 20-25 fpe. I already know what I want in the end from this pistol, so I thought it best to bring it to the ballpark pressure now, rather than getting things dialed in, then having to re-adjust. 20-25 fpe is a solid squirrel hunting pressure.

3mm hex key into this slot here to adjust the power.

Don't really know if it is exactly accurate, but in my mind, "Righty is tighty" and "Lefty is loosy". So turning right (clockwise) closes the valve and reduces the power. Turning left (counterclockwise) opens the valve and increases the power.

I think that technically, turning right increases the closing valve tension, thus reducing power, and vice versa.

For me, 6 quarter turns from closed achieves about 22 fpe’s. The exact number of turns is really not that important if you have a chronograph. Load the magazine, fire a couple of pellets, open up more pressure, repeat. Pretty much no matter what your desired pressure you will get there in under a dozen pellets.

 

[weevil]

Navig - nice posts. Regarding “tuning” for speed/power: If one is to apply your “quick tune” approach, they should do it with a median tank pressure, say 250-210 bar, because if they set at an extreme (either high or low tank pressure), it will not apply to the majority of the shots through the string.

Moreover, any user is advised to shoot a full string from a high fill pressure down to 160bar to get a sense of the relationship between tank pressure and speeds for their particular tune.

See the excellent thread from @JDGriz for more detailed info:

Huben - GK1 .25 tuning for Altaros & JSB - charts and data

I've compiled some chronograph data for the GK1 V3 in .25, with Altaros 50gr slugs. One of the data columns is with 51gr slugs, because I ran out of 50s (they are smooth-walled and this might be reducing the power by 2-3 fpe, looking at the data). Unscrewing the power screw all the way until it...

www.airgunnation.com

 

[wimpanzee]

I finally got my little folding stock in from jkarmy, it is not carbine-ated!

 

[md26]

I finally got my little folding stock in from jkarmy, it is not carbine-ated!

View attachment 441461

View attachment 441462

Hey wimpanzee, might I ask did you use the single or double 1913 adapter to mount this stock?

 

[RAMJET66]

I finally got my little folding stock in from jkarmy, it is not carbine-ated!

View attachment 441461

View attachment 441462

Do you have a link for that stock ? i like it TIA

 

[wimpanzee]

Hey wimpanzee, might I ask did you use the single or double 1913 adapter to mount this stock?

I used the double, and screw is on the lower notch. The stock also has 2 mounting holes on the folding piece, and it's on the lower.....the red dot doesn't sit very high!

Here is a link

5KU SS-8R Style with Folding Buttplate Stock and 1913 Picatinny Rail Folding Mech

Clamps on any 1913 Picatinny 20mm RailFor MPX / MCX Folding Braces / StocksFor Airsoft Only

shop.jkarmy.com

Is was about $65 shipped, and I ordered it on the Chinese new year and still got here pretty fast!

 

[md26]

I used the double, and screw is on the lower notch. The stock also has 2 mounting holes on the folding piece, and it's on the lower.....the red dot doesn't sit very high!

Here is a link

5KU SS-8R Style with Folding Buttplate Stock and 1913 Picatinny Rail Folding Mech

Clamps on any 1913 Picatinny 20mm RailFor MPX / MCX Folding Braces / StocksFor Airsoft Only

shop.jkarmy.com

Is was about $65 shipped, and I ordered it on the Chinese new year and still got here pretty fast!

Awesome thank you for the detailed reply!

 

[RAMJET66]

thanks

 

[primaz]

Wow, thanks guys, so much information and cool stuff to digest! As I have mentioned, I will get back to optics in a few posts.

@sactargetshooter , I'm in Chico baby! Lucky enough to be on my own 5 acres. The bloom from the other day, altho the windstorms of yesterday and today have pretty much ended the bloom.

View attachment 441432

We ALL HUNT squirrels. Lucky enough that I am in a community where I don't have to moderate my airguns for the sake of my neighbors.

Which does segue into my next post...

Good to see you and Sactargetshooter as I am a fellow Nor Cal shooter. I am in the Bay Area Peninsula Coastside and love shooting the .25 GK1

 

[Navig]

@weevil Very true. So much info on this thread. For sure I will circle back to chono and pressure testing. At this stage, I haven't cleaned the barrel yet, and was still using the iron sights! I fired the pistol for the first time, and was like, huh, let's get it somewhere even in the ballpark of where I want to end up. For now, just regurgitating the directions in the manual.


Plenty of awesome carbine stock mods in the wild. Looks like the pics above are sporting @moistone receiver plate. Plenty of info at the GK1 Carbine Stock mods thread. Even pics of this project nearly completed. I will get there! Just methodically posting my way step by step from the start.


But, there are some general basic critical ground rules for pressure of the GK1.

According to the manual, the Max Pressure for the pistol should be 350 bar (=25 MPa or ~5000 psi).
I typically only ever go to 310 bar (=31 MPa or ~4500 psi), because that is how high my compressor goes to. To reach 350 bar I could add pressure with my hand pump, but I haven't felt a need to do so as of yet.

You need to be careful on shooting the pressure down too low. If you fire the pistol on too low pressure, you will get a jam, as the pellet may not have enough pressure behind it to exit the barrel. While this is certainly not specific to the GK1, it is perhaps magnified because of the ridiculously broad range of power available as well as broad range of ammunition utilized. The manual suggests a minimal pressure of 120 bar. But I would imagine if you were using a very large and heavy 25 caliber tight fitting slug, you would want a higher minimum pressure to give a larger safety buffer.

For standard .22 diabolo pellets, I would say keep the pressure above 140 bar.

Would love to hear the community opinion on what general minimum pressures they would recommend.

 

[Navig]

And, lots of critical education from GK himself: