Huben Ring shaped indentations inside gk1 barrel

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Asher

Asher

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Oct 24, 2018
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Colorado, United States
Over the past year or so I have polished all the barrels on my air guns, except for my don cothran which is already super smooth. I did it to my .25 huben k1 and my .22 k1 before I sold it. Recently I did it to my .46 challenger bullpup as well. All these guns saw improved shot velocity consistency afterwards.

A few days ago I decided to do it to my gk1. The gun has been fairly accurate in the past but tended to get inaccurate as the barrel leaded and sometimes was randomly innaccurate, i would often miss a shot and think it was bad form or impatience but now i dont think so. It seemed to foul after far fewer rounds than my other guns. I am very comfortable doing barrel alignments on hubens so I finally took apart my gk1 to polish the barrel. When I took it apart I noticed what seemed to be a dark ring inside the barrel. Didn't know what to make of that and proceeded with the polish.

After polishing I naturally looked through the barrel to see how shiney it was and noticed 4 distinct ring indentations in the barrel. They definitely were there already, no way polishing put them there. No way shooting slugs did it, no way the carbon fiber un-jammimg rod or cleaning rod did it, not that i can imagine anyway. I asked Kelly, he thinks it's a manufacturer defect. I do have only the 5th one ever made. Trouble is, I've had it over a year already. Hoping I get some help. Anyone else ever see such a thing or know how it could have happened?

Here's some screenshots of some videos i took of it.
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Anyway, after the polish I shot some groups today. Just terrible. This slug can hit 1 cm targets fairly easily at 50 yards out of my .25 k1, and others who got them for their gk1s said they did well. Not now. These groups were from a full rest at a mere 15 yards, and i took my time and aimed carefully and consistently, using the iron sights can not account for how terrible these groups are:
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Those appear to be bulges, based on the pictures. The rifling ramps up into the bulge and then back down to strait wall sides. I've seen this on a big bore where it appeared that a shot slug slammed into another stuck round, causing a bulge upon impact. Do you have a micrometer to get a precise reading of the outside of the barrel? If so, test size before, at, and after the ring's to see if the outside has expanded a little?

With that change in accuracy, it will likely require a new barrel unless you can polish a long choke into it. My GK1 barrel has sone "rough" cut rifling. It would be nice to get a bunch of good barrels made for them at exacting tolerances; as some barrels seem to be way better than other's in the accuracy department.
 
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Asher said:
I don't have a bore scope or i would.

They are definitely indentations not bulges, or i would've felt them offer resistance as I polished the barrel.

I have some digital calipers i could try though.

Don't think I've ever had a stuck projectile that another has slammed into
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When I say bulges, I mearn that the barrel has expanded (bulged) from the inside out, and what you are referring to as indentations. There won't be any felt resistance, because the ringed bulges are bigger in diameter. What you would feel, as I did, is whatever you push down the bore going by the bulged expanded rings will pass by easier with less resistance.
 
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Airgun-hobbyist said:
When I say bulges, I mearn that the barrel has expanded (bulged) from the inside out, and what you are referring to as indentations. There won't be any felt resistance, because the ringed bulges are bigger in diameter. What you would feel, as I did, is whatever you push down the bore going by the bulged expanded rings will pass by easier with less resistance.
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Oh gotcha, right. Well, I can't say i noticed any difference in resistance at all.

Kelly said huben doesn't ship barrels by themselves, plus they are likely on holiday for Chinese new year right now. I will be quite upset if the only solution is a brand new gk1, especially if newer ones don't like .254 diameter slugs and I have to get a new swage die too.

The only time slugs have jammed in the barrel is whennits been near the breech and the magazine won't rotate and usually the gun dumps it's air, and I've had to fix the jam and refill it first. ( after the newer spring setup and modifying the ring around it this hasn't happened to me)
 
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i was a little surprised yesterday that after looking for and finding parts diagrams the barrels are not a part on the list
so it should be able to be replaced but they do not sell them?
someone could make you an LW barrel but with a new blank and labor to size and thread it would not be cheap
i would ask for a new barrel out of warranty or not

and why is a barrel and the mag and breech worth 600 bucks now that is absurd
 
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If the bulges can be seen or measured on the outside, they do look like what happens when a slug is stuck and another slams into it. If the outside diameter shown or measures with no bulge, then something strange happened in manufacturing. The fact that the rifling lands appear of even depth suggests the barrel was rifled before the bulges came about.

If the OD is smooth, then the OD of the barrel was machined after the damage occurred. Else, the damage most likely occurred on the fully assembled gun (or barrel test bench). The question is, did the damage happen in the factory, dealer or due to the owner, or prior owner doing something to so cause it to bulge. Such as shooting into a cleaning rod left in the barrel; or just a stuck projectile. Whatever it was, it happened more than once.
 
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Seems well reasoned. I will be checking the OD soon, assuming digital calipers are sensitive enough. I did find that wolfiek huben seller in Spain sells barrel and magazine assemblies, but yeah they're about 600.

Can't recall ever shooting a slug into a stuck one but can't think of anything else that could do this.

A few years back, i helped out a rep from wolfiek at an airgun event at the Rio Salado range in Mesa Arizona. Lots of the airgun youtubers were there, I happened to be there just shooting. Anyway, a rep from wolfiek was there to compete with his huben k1 and had come all the way from Spain and forgot his fill probe. No one else at the event had a huben. I let him borrow mine. I had to leave before the event finished so he had to mail me my probe after, and I think he sent a discount card too as a thanks for saving his bacon. Never thought I'd have a reason to buy anything from them but I can't find anyone else that sell gk1 barrels. Just gotta look through my stuff and find that discount...
 
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Airgun-hobbyist said:
Those appear to be bulges, based on the pictures. The rifling ramps up into the bulge and then back down to strait wall sides. I've seen this on a big bore where it appeared that a shot slug slammed into another stuck round, causing a bulge upon impact. Do you have a micrometer to get a precise reading of the outside of the barrel? If so, test size before, at, and after the ring's to see if the outside has expanded a little?

With that change in accuracy, it will likely require a new barrel unless you can polish a long choke into it. My GK1 barrel has sone "rough" cut rifling. It would be nice to get a bunch of good barrels made for them at exacting tolerances; as some barrels seem to be way better than other's in the accuracy department.
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Nooo, NOT bulges. Unless you consider them...bulging...outward.
A CLOSE look at picture #4 is pretty clear which way the material goes.

But, yeah, very odd indeed.

Mike
 
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MikeVV said:
Nooo, NOT bulges. Unless you consider them...bulging...outward.
A CLOSE look at picture #4 is pretty clear which way the material goes.

But, yeah, very odd indeed.

Mike
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My characterization of a "bulge" is that the inner wall has bulged outwardly, making the inside diameter larger at the noticable ring. I have a 357 barrel that has a single ring in it just like this, probably from a previous owner shooting a projectile into a stuck projectile. When they slam together something gives somewhere. And if a hollowpoint is slamming squarely into the back of a stuck round it is going to try and expand around the back of said round and with a good amount of force tbe thin barrel wall is going to give.
 
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What will really suck is if the new barrel doesn't like .254 slugs and I have to get yet another swage die. Fingers crossed.

Don't think I'll ever rapid fire again, although, I was thinking, maybe a slug impacted in the barrel one of the times the gun double fired. At one point I had the trigger set to break at a fairly light weight, and I've found that, on mine at least, the screw that adjusts that can work itself loose over time and shooting, and I had it get so loose that it double fired a few times. Since getting the updated spring setup, modifying the ring around it, and making the trigger break weight a bit heavier, I've had no issues with it in terms of functionality, no jams. So here's hoping this is the last problem I ever have with this gk1
 
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Asher said:
Doubt it theyre pure lead and the same that I shoot from my k1. In both of them I see better accuracy with 254 than with 253, although I do still have a 2537 die that I don't use. The old barrel also shot 254 better than 2537 as well though
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I have a red dot on my .25 gk1 I have for close encounter so accuracy is more of my problem than ammunition..but at 30 yards with the red dot I'm 1moa right inside the square of the paper targets. And these are the speeds I'm getting maxed out I have it for power shots not shot count. This was from 350 bar to 270 bar.....I have the v3+ have not tried .254

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