Another Huben GK1 .25 ammo thread

[ikaros]

Got my GK1 and been having a lot of fun with it.

I have the SLX 3x mounted on the dovetail with the longest cantilever mount it comes with which is just not enough with its 2ish inch eye relief.

Unfrozen my v3 gk1 does not have the forward screw, which prevents me from mounting the currently available top pic rails, so I have a v1 rmr mount + rmr to pic rail adapter to bring it further back.

I’m currently limited to a 305ish bar fill but I have a pump on order to top it off to 350.

I have found ~56/55FPE on the first shot to be a nice sweet spot for getting through a whole mag without too much drop and a very consistent string of 10ish shots or so.

Here is a shot 17 shot string with Zan 33gr .253 slugs.

I have only tried 2 ammo types atm: 33gr .253 zan slugs and 33.95gr King Heavy Diabolo MK11 pellets.

The pellets are much more accurate.

Here is a 6 shot string at 18 yards with the zan slugs starting at a a 300bar fill:

Here is a 6 shot group starting at 300bar fill with the pellets.

I have jsb knockout mk11 slugs with flared skirts on order.

I would love to use slugs for the much better BC and will continue to search for a 33gr ish slug that can match the accuracy of pellets.

 

[JaceSpace1369]

Got my GK1 and been having a lot of fun with it.

I have the SLX 3x mounted on the dovetail with the longest cantilever mount it comes with which is just not enough with its 2ish inch eye relief.

Unfrozen my v3 gk1 does not have the forward screw, which prevents me from mounting the currently available top pic rails, so I have a v1 rmr mount + rmr to pic rail adapter to bring it further back.

I’m currently limited to a 305ish bar fill but I have a pump on order to top it off to 350.

I have found ~56/55FPE on the first shot to be a nice sweet spot for getting through a whole mag without too much drop and a very consistent string of 10ish shots or so.

Here is a shot 17 shot string with Zan 33gr .253 slugs.
View attachment 467308

I have only tried 2 ammo types atm: 33gr .253 zan slugs and 33.95gr King Heavy Diabolo MK11 pellets.

The pellets are much more accurate.

Here is a 6 shot string at 18 yards with the zan slugs starting at a a 300bar fill:

View attachment 467309


Here is a 6 shot group starting at 300bar fill with the pellets.

View attachment 467310

I have jsb knockout mk11 slugs with flared skirts on order.

I would love to use slugs for the much better BC and will continue to search for a 33gr ish slug that can match the accuracy of pellets.

In my case I have found the huben barrels prefer the .254 sized slugs

 

[ikaros]

In my case I have found the huben barrels prefer the .254 sized slugs

I just ordered many avs varieties in this caliber. Which di you use? Do you have any shot group pics?

 

[JaceSpace1369]

I just ordered many avs varieties in this caliber. Which di you use? Do you have any shot group pics?

No I do not, I currently have a gk1 in .22 but had a K1 in .25 from @gendoc I was able to take iguanas out to 178yds with the gun. I tried the 253 zans and tried the 254 NSA and the 38.5gr outshot them by a considerable margin.

 

[ChuckHunter]

Why are you worried about BC in a 8 inch barreled unregulated pistol?
I understand the cool factor of slugs but these guns were designed for pellets!
Accuracy and consistency trumps all in my book. I have a V1 tuned to 800fps with a spread of only 8fps over a full mag of 17 shots with JSB heavies Mk11 pellets.
320 bar down to 200 bar and shooting starlings out to 50 yards with authority!
BC really only comes into play at long range and needs very consistent speeds to be affective!

 

[brawler1588]

For an unregulated package there definitely will be a sweet spot. I as well wanted to find what ammo did best so I tried the hades 25.39gr and the jsb 33.95gr I will attach the video I did at 25y and while they did good I wanted tighter so I was going to find the speed sweet spot and adjust. The day I was doing that testing I decided to try the h&n baracuda hunters because they are my choice in the k1 as well and bam 2 mags and a better shot group all around.

 

[TiPascal]

Nice, what tune did you end up with that you liked?

Also, what zoom were you using? The video was pretty good for a digital zoom unless it was at 5x.

 

[ikaros]

For an unregulated package there definitely will be a sweet spot. I as well wanted to find what ammo did best so I tried the hades 25.39gr and the jsb 33.95gr I will attach the video I did at 25y and while they did good I wanted tighter so I was going to find the speed sweet spot and adjust. The day I was doing that testing I decided to try the h&n baracuda hunters because they are my choice in the k1 as well and bam 2 mags and a better shot group all around.

View attachment 467760

Im jealous of your pic rail. To be clear your baracudas did not make it to the video?

 

[brawler1588]

Im jealous of your pic rail. To be clear your baracudas did not make it to the video?

Yes that was the first day of testing and it was only the hades and 33.95gr I don't think I have enough to make another vidoe so I will drop it here for you. I wasn't 100% stable and think I can still tweak it tighter but all and all I was happy with it.

 

[ikaros]

Awesome shooting, thank you. I will have to check them out. Around the 40 second mark of the second video I noticed you got some POI shift up and right. Any idea what that was due to?

 

[JaceSpace1369]

Yes that was the first day of testing and it was only the hades and 33.95gr I don't think I have enough to make another vidoe so I will drop it here for you. I wasn't 100% stable and think I can still tweak it tighter but all and all I was happy with it.

I too found that the hunter extremes shoot extremely well out of my gk1 .22.

 

[ikaros]

update:

Both 33.6gr and 38gr NSA .254 slugs, which actually measure .255 at the base, shoot amazing out of the GK1

They have an R4 BC ~.088 with the first shot at 860ish fps and the 17th shot at 815ish fps when starting with a 350bar fill.

The accuracy is very very good.

I tried AVS .254 slugs, which come in measuring at a true .254, but they do not shoot well at all. I ordered some .2553 slugs to test. The GK1 seems to really like .255 ammo.


If you are looking to tune your .25 GK1 for maximum performance out of a single magazine with a full 350bar fill, 32gr to 36gr is a very good sweet spot for your ammo.

38gr or higher shoot well, but the velocity will be too low imo, with first shot at 825 fps or lower.

I will post some shot groups in the coming days.