Huben .25 Slugs for GK1?
- Thread starter FLgunner
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Yeah sounds like .250…you will be good with the NSA .254’s.Here’s a couple other good alternatives.
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I looked and the NSA site and they make both the 38.5 hollow point flat base and a 33.5 hollow point cup base. Which NSA slug do you think is a better for accuracy and hunting?
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The Hawki Thunder domed 33.95gr fits wonderfully in my Gk1, but haven't tested for accuracy as of yet. But those are the ones thst look like a pellet slug hybrid
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I noticed the h@n hornets 22.07 grain are very loose im going to try a couple coats of Industrial blaster dry silicone oil to see if that helps, I noticed they come also in 24gr maybe that would help in mass but we,ll have to see
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These were recommended to me. I have a ox of them. Flawless. https://airguntactical.com/products...2&_sid=36fcf6035&_ss=r&variant=42274598289558
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From reading it seems like most people are having decent performance as long as the slugs are .254 in size? AVS slugs makes them in flat, cupped, dished, and hollow based. Has anyone found which works best with the GK1 as far as the type of base if the cupped, dished or hollow base is better than the typical flat base slugs? When I read posts in the projectile forum it sounds like it is dependent on the type of gun and barrel which is why I am curious if anyone has gone beyond just the diameter but tried the different types of bases that can be purchased to see if one design is better?Yeah sounds like .250…you will be good with the NSA .254’s
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.254 Diameter CUP 25 Caliber Slugs - Hollow Point (28 to 48 Grains) 100 count - AVS Slugs
100 count - .254 Diameter Hand Swaged Lead Slugs (28 to 48 Grains)
avsslugs.com 
.254 Diameter DISH 25 Caliber Slugs - (28 to 48 Grains) 100 Count - AVS Slugs
100 count - .254 Diameter Hand Swaged Lead Slugs (28 to 48 Grains)
avsslugs.com 
.254 Diameter HOLLOW BASE 25 Caliber Slugs - Hollow Point (28 to 48 Grains) 100 count - AVS Slugs
100 count - .254 Diameter HOLLOW BASE Hand Swaged Lead Slugs (28 to 48 Grains)
avsslugs.com Upvote 0
I looked at the link and they do have them in .254 diameter; I hope you purchased that diameter as the .250 will likely be too lose and could cause jams? Post some pics of your results and shot string FPS
Those are offered at 33 and 38 grain so they are the same weight as the JSB pellets I am using so that should produce good FPS and am curious as how they perform at longer distances vs the JSB pellets of similar weightsUpvote 0
You folks have to do some arithmetic. No slugs that I am aware of fit correctly in a GK1. This is because the magazzine has no way of securing them in position and they usually have too much bore resistance for the available pressure. Simply, the gun is designed for pellets. Now, I have stated this in other threads and I will do this here one more time. The GK1 barrel diameters are Land = .247", Groove = .253". The magazine bore size is exactly .250".The magazine at the rear of each bore has a small chamfer. This chamfer is designed to capture the tail end of a Diabolo pellet skirt, which just happens to be .260".It is that chamfer that retain the pellet in position while in the magazine. Slugs do not have .260 skirt. Slugs also have a much longer bearing surface that must be pressed, forged or swaged into the barrel, where a pellet head just touches the barrel lands for stability and the skirt is swaged first in the magazine at firing time to .250" and then as it enters the barrel, the skirt is then swaged from .250" down to .247" to conform to the rifling lands. Remember that you have only 300 bar to achieve this swaging, whereas in a powder burner you have somewhere between 25,000 CUP (copper units of pressure)in a pistol to just over 50,000 CUP in rifle cartridges.
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Griffin slugs are really sweet.From reading it seems like most people are having decent performance as long as the slugs are .254 in size? AVS slugs makes them in flat, cupped, dished, and hollow based. Has anyone found which works best with the GK1 as far as the type of base if the cupped, dished or hollow base is better than the typical flat base slugs? When I read posts in the projectile forum it sounds like it is dependent on the type of gun and barrel which is why I am curious if anyone has gone beyond just the diameter but tried the different types of bases that can be purchased to see if one design is better?
.254 Diameter CUP 25 Caliber Slugs - Hollow Point (28 to 48 Grains) 100 count - AVS Slugs
100 count - .254 Diameter Hand Swaged Lead Slugs (28 to 48 Grains).254 Diameter DISH 25 Caliber Slugs - (28 to 48 Grains) 100 Count - AVS Slugs
100 count - .254 Diameter Hand Swaged Lead Slugs (28 to 48 Grains).254 Diameter HOLLOW BASE 25 Caliber Slugs - Hollow Point (28 to 48 Grains) 100 count - AVS Slugs
100 count - .254 Diameter HOLLOW BASE Hand Swaged Lead Slugs (28 to 48 Grains)
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Steve, great information. So, am I understanding this correct, many people say that the .254 slugs shoot well in their opinion, but from reading your information that diameter may be find going down the barrel but if the magazine is .250, then my assumption is every shot is putting wear on the narrower magazine? Is that right? so while they may be able to shoot those .254 slugs then the magazine will slowly get worn and then pellets might fit too loose after a lot of slug shooting? and if you shoot .250 slugs I have read people having jam issues since the slut is too loose in the magazine and that would be due to no skirt like a pellet. Am I understanding this correctly?
For me I am very happy just shooting my JSB Match Diablo pellets as they shoot great, don't jam and buying them in larger packs of 4 at a time they are inexpensive for both 25.39 and 33.95 grain. I have my FX M3 to shoot more power and slugs with their liner made for slugs. The Huben GK1 is great but maybe it is best to try not to make it an everything gun, shoot enjoy it for pellets as slugs to me are for hunting long range and better then to use a rifle....
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The only way a slug, when loaded into the GK1 magazine, can remain fixed in place without shifting around and potentially jamming up the gun is if the slug diameter must be larger than the .250" bore because slugs do not have a flared skirt that seats in the chamfer. When the slug is then fired the slug must be swaged into the barrel which is again smaller than the slug. The net effect is a slug which now has a bearing surface with the barrel much longer than that of a Diabolo pellet with a lot more resistance. The amount of resistance is also effected by the slugs lead alloy. Believe me when I say there are a myriad amount of lead alloys in use that range from RN11 to RN28 (from memory) in hardness. This can cause excessive wear and fouling. How much more I cannot say, but it is not very good for the gun in any case. When I was younger, I shot silhouette pistol in competition and the effective life of a barrel was not much more than about 5,000 rounds before it was worn out ( S&W Model 29 44 Mag) I shoot now more than 10,000 pellets a year At the end of the day, it's your gun do as you wish.
I use JSB pellets in my GK1s just like you. Mostly the 25 gr because of cost. Yesterday I dropped a crow out of a tree a little more than 100 meters away off hand using about 3 MOA of holdover. My gun was zeroed in at 25 meters. . . . . Who needs slugs?.
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AVS has .253 now. I tried to push it and bought AVS .253 cup 48 grain listed at .429 long. They are just a tiny bit too long and scrape a bit when I rotate my GK1 magazine, so I didn’t try to fire them. I have Zan 38grain to try, but will probably also get a slightly shorter AVS to try to max it out.
Also, I found it interesting that my new GK1 v3 power was turned down basically all the way when I received it. Maybe to meet other market requirements? It was quiet and a lot of shots per fill, but the sight was raised to max for short shots! I now have it up to around 650fps depending on what’s loaded, but I’ll turn it up when I try the slugs.
Also, I found it interesting that my new GK1 v3 power was turned down basically all the way when I received it. Maybe to meet other market requirements? It was quiet and a lot of shots per fill, but the sight was raised to max for short shots! I now have it up to around 650fps depending on what’s loaded, but I’ll turn it up when I try the slugs.
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Just a few items to share related to what @dflo wrote.
Based on what I have read and Strelok, the gyroscopic stability of a projectile has to do with rate of rotation and the length of the projectile. A longer (and heavier) slug works against GS. That said, there is no harm in giving it a try!
Second, while the GK1 power adjuster is very flexible in a sense, getting a flat(ter) curve of tank pressure vs. muzzle velocity is tricky. Unlike a regulated "traditional" PCP with hammer spring tension and regulator adjustments, the GK1 cannot be tuned to get a low extreme spread shot spring over any desirable muzzle velocity. I am still getting the hang of how the power adjuster affects the velocity-pressure curve. This (https://www.airgunnation.com/threads/gk1-25-tuning-for-altaros-jsb-charts-and-data.1305578/) is a good introduction. You can see how the flatter shot strings are around 700 FPS for the .25 GK1. Mine is a .22, and the flatter shot strings are around 850 GPS. I will get getting some very light pellets to experiment with the theory that the GK1 has an intrinsic low-ES velocity that is based on the caliber.
I am still learning (and thinking), so take my understanding with a grain of salt!
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On a different note, I just got the Zan rounds and found them to be TIGHT. i had to push them in. the mag cycles fine but im still afraid to shoot them. should i be?
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my testing agrees with the low to mid 700's for the flattest power curve in the .25 V3 Gk1. I was looking to min mx the extreme spread with the highest possible fpe for 1 full magazine of 17 shots. My best results after testing nearly a thousand rounds across a dozen different slug weights, head sizes, and brands was the 41 grain zans at 734-750 fps, for 17 shots all above 50fpe. this shot string starts at 300bar and ends at 19bar. I should have taken notes on exactly how many turns it took to get there, but I started at two full turns up from min and adjusted 1/8 of turn after each magazine until the curve flattened. Also, I still occasionally get a slower first shot, (like 690 fps, before it jumps back up to 750, doesn't always happen but it drags the spread to 60 when it does) not sure if thats due to filling above where I normally do, might have been up to 310 bar or the valve sticking a bit after sitting when reloading and refilling. Will be doing more testing this week once I get more deliveries of the other slugs I ordered to test with as the accuracy of all the slugs ive tested outside of fx hybrids is pretty crap at this low speed. So while its speed and power are consistent, the group is 2 inches at 25 yards, which is not ideal.
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That makes sense because the cross section area of a .25 is about 30% more than that of a .22. The current "happy point" (flattest shot string) of the .22 GK1 shooting 22 gr pellets is about 870 FPS. 870:700 is about 1.24, roughly agreeing with the 30% increase of cross section area of the barrel. The power wheel setting is about 1.75 rev. CCW from the min position, also roughly agrees with @killraven4334 's setting. My shot string is from a 325 bar fill, shooting down to about 210 bars for one clip (19 shots).
The interesting part is that 870 FPS is also the "happy point" for light pellets like GTOs and HN FTTGs. The power wheel setting is about 0.75 rev. CCW from min for the lighter pellets. The shot count does increase with lighter pellets.
All of these observations are consistent with the theory that it takes a flow of about 400 cubic inch per second (870 FPS * 12 in/ft * 0.11 in^2 * 3.14) to have any significant effect on the closing valve actuating faster. It'll be interesting when the .177 version is available because this calculation puts the MV to above the speed of sound in order for a .177 to achieve the same flow rate. Huben can probably tune a few variables for the .177 version to have a flat shot string centered around 950 FPS.
I have also observed the first shot being slower, but not that much these days. If projectiles are wet-lubed, that can partially explain it because the lube may get viscous as it dries in the barrel. I dry lube my pellets using a PTFE spray where the solvent/carrier dries before I load the pellets.
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