Disclaimer
What I do with my gun may void the factory warranty, and/or pose risks to property damage or personal injury. The outcomes of what I do with my gun may differ in your case!
Overview
A little expensive for an air pistol, and some people will be quite annoyed or frustrated by the gun jamming. However, it is a capable and versatile platform capable of plinking at low muzzle energy or sniping at 100 yards.
Overall, I do not recommend this pistol to people who do not want to open up a PCP pistol. It will jam due to user errors occasionally, like grinding gear with a manual transmission. Also, in my case, to get most out of the pistol, I had to work on the barrel and calibrate the barrel-magazine alignment.
That being said, for people who are comfortable with disassembling PCP airguns and using common tools like a Dremel, the GK1 is a great platform!
The jam
I don't think anyone can avoid a jam with this pistol, period! Clearing a jam with a disassembly down to the barrel-magazine subassembly is relatively easy for people who feel comfortable with working with PCP guns. Of course, safety first! Make sure the gun is completely degassed first. Other than that, there are no surprise springs or little detent balls to fly out!
Feeding the right ammo is the first step to minimize jamming. For low-energy applications, I find the HN Field Target Trophy Green and GTO lead-free pellets very reliable. For mid-range applications, the JTS 22gr .22 pellets work great. And for long range, AVS 22gr .223 slugs shoot well out of my GK1.
Of course, try to remember to return the lever that releases the magazine for free rotation. I cannot count the number of times that I forget to do that!
The barrel
For a non-LW and non-CZ barrel, the Huben barrel is actually surprisingly good! Unfortunately, mine came with a little bit of burr on both ends of the barrel. Nothing major, but enough to cause accuracy issues shooting only out to 10 yards.
Using a lit loupe to inspect the leade and crown of the barrel, I identified the burrs. I don't have a lathe. Using a rotary tool that has a variable speed and a rubber tip with embedded abrasives, the burrs can be removed. The key is being slow and gentle. Err on the side of "maybe that is not enough", inspect again, and work on the burrs a little more.
I also fire lapped the barrel using the AVS slugs and Mother's polish. I cannot provide a before-and-after comparison of just fire lapping. In other words, it may not have made any difference!
I can say that after all the treatment, pushing an AVR slug through the barrel (after a little bit of initial tapping from the leade side) has consistent resistance all the way through. As one of my airgun buddies would say: the barrel is not choked, the entire barrel is a (gentle) choke!
The barrel-magazine alignment
The two lower bolts that hold the barrel subassembly and the magazine subassembly together are meant to have some play. From factory, the alignment was just a little bit off. I also found that pellets are more forgiving compared to slugs. Before I made this observation, I was able to shoot slugs quite accurately, but not slugs. In fact, I was about to give up on slugs, all together, at one point.
To properly align these two subassemblies so that the barrel and the magazine are concentric, use a longer slug. The 22gr .22 AVR slug is too short to make the alignment. Even with a slug intentionally stuck between the magazine and the barrel, the subassemblies will continue to have play, but this time rotating around the slug (just a little!). This is fine. I just visually line up the subassemblies before tightening the bolts. Don't over tighten, either!
This alignment is what finally helped achieve 2 MOA accuracy at 100 yards. I will describe that later.
I am not a pistol shooter!
Fine, I admit it!
The GK1 can be turned into a little carbine (or as some people insist, a pistol with a shoulder stock!). Personally, I think the shoulder stock definitely helps to bring out the full potential of this little gun with an 8" barrel. Ethan D's lower pic rail is also essential to extract the last bit of accuracy.
When it is all said and done, the pistol-with-a-should-stock configuration weighs a hair more than 4 pounds. This is with the following: shoulder stock adapter, folding shoulder stock, 5x24 Immersive scope, a laser intended for pistols, and a Huma LDC.
I can definitely still feel the recoil if I shoot the AVS slugs at 36 FPE!
How accurate is the GK1?
As delivered, not so good. Mine was getting 0.4" to 0.5" groups at 10 yards. At 10 yards! My little humble PP800R does better than that with a red dot!
However, with everything mentioned done, even using a 5x24 Immersive scope with a chevron reticle and thick dots for hold over, I was shooting groups within 2-3" (side-to-side) at 120 yards with the AVS slugs (36 FPE muzzle energy). This is with some cheating: the gun was attached via Ethan's lower pic rail to a mini tripod, and I was sitting on the ground. No benches, no rests if my own knee does not count as a rest!
I should probably conduct a proper accuracy test with a better scope and have the gun rested on a bench. I have confidence that the GK1 will shoot even more accurately given the environment intended for precision shooting.
Some people may say that this does not come close to the accuracy of the FX Dynamic, Huben's own K1, Daystate's Redwolf, AGT's Uragan, etc. They are not wrong! But the GK1 is light, compact, and extremely pointable. In all fairness, my opinion is that the GK1 punches above its class.
How versatile is the GK1?
36 FPE muzzle energy is not necessary for a lot of closer range applications. Turning the power adjuster instantly transforms the 36 FPE gun to a 7.5 FPE "plinker" shooting light pellets. For my specific GK1, 1.75 revolutions CCW from the minimum power position gives one clip of 36 FPE shots shooting AVG 22gr .223 slugs (from 330 bars to 210 bars). 0.5 resolutions CCW from the minimum power setting position gives me two clips shooting the HN FTTG lead from pellets at about 7.5 FPE. One clip is 19 shots.
Minor gripes
The fill ports are not covered. I just use two pieces of gaffer tape to cover the two ends. Not a huge deal, just a minor gripe.
Given the recoil (hence muzzle flip), I wish the grip is better designed to help mitigate recoil/flip. The factory grip is not bad, but not optimal, either.
No included lower-pic rail. I do not recommend a airtube mounted lower pic rail for accuracy because there is some play between the airtube and the receiver. Ethan's lower pic rail that attaches to the stout trigger guard is a good solution. I just wish that this comes with the gun. I know, I know, this is a pistol!
The 7mm hex key needed to open up the end cap is also, well, annoying. I understand the design decision, however.
This is getting long, maybe I should just post it now!
What I do with my gun may void the factory warranty, and/or pose risks to property damage or personal injury. The outcomes of what I do with my gun may differ in your case!
Overview
A little expensive for an air pistol, and some people will be quite annoyed or frustrated by the gun jamming. However, it is a capable and versatile platform capable of plinking at low muzzle energy or sniping at 100 yards.
Overall, I do not recommend this pistol to people who do not want to open up a PCP pistol. It will jam due to user errors occasionally, like grinding gear with a manual transmission. Also, in my case, to get most out of the pistol, I had to work on the barrel and calibrate the barrel-magazine alignment.
That being said, for people who are comfortable with disassembling PCP airguns and using common tools like a Dremel, the GK1 is a great platform!
The jam
I don't think anyone can avoid a jam with this pistol, period! Clearing a jam with a disassembly down to the barrel-magazine subassembly is relatively easy for people who feel comfortable with working with PCP guns. Of course, safety first! Make sure the gun is completely degassed first. Other than that, there are no surprise springs or little detent balls to fly out!
Feeding the right ammo is the first step to minimize jamming. For low-energy applications, I find the HN Field Target Trophy Green and GTO lead-free pellets very reliable. For mid-range applications, the JTS 22gr .22 pellets work great. And for long range, AVS 22gr .223 slugs shoot well out of my GK1.
Of course, try to remember to return the lever that releases the magazine for free rotation. I cannot count the number of times that I forget to do that!
The barrel
For a non-LW and non-CZ barrel, the Huben barrel is actually surprisingly good! Unfortunately, mine came with a little bit of burr on both ends of the barrel. Nothing major, but enough to cause accuracy issues shooting only out to 10 yards.
Using a lit loupe to inspect the leade and crown of the barrel, I identified the burrs. I don't have a lathe. Using a rotary tool that has a variable speed and a rubber tip with embedded abrasives, the burrs can be removed. The key is being slow and gentle. Err on the side of "maybe that is not enough", inspect again, and work on the burrs a little more.
I also fire lapped the barrel using the AVS slugs and Mother's polish. I cannot provide a before-and-after comparison of just fire lapping. In other words, it may not have made any difference!
I can say that after all the treatment, pushing an AVR slug through the barrel (after a little bit of initial tapping from the leade side) has consistent resistance all the way through. As one of my airgun buddies would say: the barrel is not choked, the entire barrel is a (gentle) choke!
The barrel-magazine alignment
The two lower bolts that hold the barrel subassembly and the magazine subassembly together are meant to have some play. From factory, the alignment was just a little bit off. I also found that pellets are more forgiving compared to slugs. Before I made this observation, I was able to shoot slugs quite accurately, but not slugs. In fact, I was about to give up on slugs, all together, at one point.
To properly align these two subassemblies so that the barrel and the magazine are concentric, use a longer slug. The 22gr .22 AVR slug is too short to make the alignment. Even with a slug intentionally stuck between the magazine and the barrel, the subassemblies will continue to have play, but this time rotating around the slug (just a little!). This is fine. I just visually line up the subassemblies before tightening the bolts. Don't over tighten, either!
This alignment is what finally helped achieve 2 MOA accuracy at 100 yards. I will describe that later.
I am not a pistol shooter!
Fine, I admit it!
The GK1 can be turned into a little carbine (or as some people insist, a pistol with a shoulder stock!). Personally, I think the shoulder stock definitely helps to bring out the full potential of this little gun with an 8" barrel. Ethan D's lower pic rail is also essential to extract the last bit of accuracy.
When it is all said and done, the pistol-with-a-should-stock configuration weighs a hair more than 4 pounds. This is with the following: shoulder stock adapter, folding shoulder stock, 5x24 Immersive scope, a laser intended for pistols, and a Huma LDC.
I can definitely still feel the recoil if I shoot the AVS slugs at 36 FPE!
How accurate is the GK1?
As delivered, not so good. Mine was getting 0.4" to 0.5" groups at 10 yards. At 10 yards! My little humble PP800R does better than that with a red dot!
However, with everything mentioned done, even using a 5x24 Immersive scope with a chevron reticle and thick dots for hold over, I was shooting groups within 2-3" (side-to-side) at 120 yards with the AVS slugs (36 FPE muzzle energy). This is with some cheating: the gun was attached via Ethan's lower pic rail to a mini tripod, and I was sitting on the ground. No benches, no rests if my own knee does not count as a rest!
I should probably conduct a proper accuracy test with a better scope and have the gun rested on a bench. I have confidence that the GK1 will shoot even more accurately given the environment intended for precision shooting.
Some people may say that this does not come close to the accuracy of the FX Dynamic, Huben's own K1, Daystate's Redwolf, AGT's Uragan, etc. They are not wrong! But the GK1 is light, compact, and extremely pointable. In all fairness, my opinion is that the GK1 punches above its class.
How versatile is the GK1?
36 FPE muzzle energy is not necessary for a lot of closer range applications. Turning the power adjuster instantly transforms the 36 FPE gun to a 7.5 FPE "plinker" shooting light pellets. For my specific GK1, 1.75 revolutions CCW from the minimum power position gives one clip of 36 FPE shots shooting AVG 22gr .223 slugs (from 330 bars to 210 bars). 0.5 resolutions CCW from the minimum power setting position gives me two clips shooting the HN FTTG lead from pellets at about 7.5 FPE. One clip is 19 shots.
Minor gripes
The fill ports are not covered. I just use two pieces of gaffer tape to cover the two ends. Not a huge deal, just a minor gripe.
Given the recoil (hence muzzle flip), I wish the grip is better designed to help mitigate recoil/flip. The factory grip is not bad, but not optimal, either.
No included lower-pic rail. I do not recommend a airtube mounted lower pic rail for accuracy because there is some play between the airtube and the receiver. Ethan's lower pic rail that attaches to the stout trigger guard is a good solution. I just wish that this comes with the gun. I know, I know, this is a pistol!
The 7mm hex key needed to open up the end cap is also, well, annoying. I understand the design decision, however.
This is getting long, maybe I should just post it now!
