Tuning Huben K1 Accuracy Tuning Tip

[mtnGhost]

I got a Huben K1 (2020 .22cal) last week. Tested it for the first time on Friday, and realized that it was getting quite a few flyers.

Then, I started to realize the flyers were happening in a pattern. I pinned most of the issues down to 5-6 specific magazine chambers. Spent that following Saturday learning how to disassemble and reassemble the rifle (mega thanks to Gregor Kamensek's long videos), and I wound up polishing the barrel and inspecting the magazine closer. 

Sure enough, when I pushed slugs through the mag chambers that I marked as suspect, they were taking pretty bad bites out of them, leaving uneven and pretty narly rifling marks. Some of the chambers had serious burrs, so I de-burred and polished them all. I also went in and polished a very light chamfer in the insertion side, some of them were super rough to load.

The results of that effort have appeared to pay off - there's a LOT less flyers now and it's grouping tighter. I was only able to get ~45 total minutes of trigger time in today, shooting at 91m / 99.5y in 15-40mph ice cold / wet winds, but when I finally got it re-tuned - the groups were tighter than they were in the dead calm winds that I had on Friday! 

Shooting the 28.5gr Varmint Knockers (1042fps avg today), unlubed / unsorted. My rifle has been the most accurate this far at 1076fps (It may even be more accurate at 1100+ - time will tell). it just seems the faster I shoot, the tighter they group, so the higher velocities are definitely worth testing

It should make for a nice little night time varmint blaster with the Nvision NOX 18 

 

[harrymoreland]

, The Huben fan club is growing.

 

[B7B]

Smart approach about the fliers. That's science. Good job!

 

[Feinwerk]

Sounds like some excellent field engineering, diagnosis, and modification. This is of good general value to all magazine fed pcp's....push pellets through and check for burrs and gouging. Yours may also have been liberating lead filings from the scraped pellets.

Great catch, thanks for sharing!

 

[randy_68]

good find on the mag issue. I have rebuilt and tuned several of these and the loading side edge of the mag has been a problem on most of them by scraping the pellets as you load them. It also causes to mag to hang up as the pellets back out from recoil then get stuck because of the sharp edge. That's when they hang up on the upper left side of the breech. No issues after fixing that. Polishing the barrel lead, crown and bore helps too..also checking mag alignment to bore. I have had some that it was off big time. 

 

[Jammin22]

Yes, that is something we do when we service one. Chamfering the loading side of the mag. makes it easier to load as well. Another thing that we check is mag. to barrel alignment. They are well built air rifles. I just installed a Huma Reg. in my Dads yesterday with great results. Enjoy. 

 

[MACTEN]

Does yours have rifling in the cylinders as the older versions did? I have the .25 and there aren't any in mine. In fact mine seems to have some kind or rubberized coating in them, but they are smooth.

 

[Ezana4CE]

@mtnghost Nice looking rifle and great post! Thanks for sharing. I don’t think I’d have thought to look for burs or chamfering in the mag. What did you use to polish it?

@randy_68 I’ve had a similar issue with pellets scraping the magazine (front and back) while loading and indexing to the next chamber. This occurred in a .25 Brocock/Daystate Mag with H&N Barracudas. At first I though it was the mag until I tried JSBs. They fit perfectly, so the issue was the ammo/mag combination. Did you find a similar issue or did your problem persist with different brands and types of ammo?

 

[mtnGhost]

@mtnghost Nice looking rifle and great post! Thanks for sharing. I don’t think I’d have thought to look for burs or chamfering in the mag. What did you use to polish it?

@randy_68 I’ve had a similar issue with pellets scraping the magazine (front and back) while loading and indexing to the next chamber. This occurred in a .25 Brocock/Daystate Mag with H&N Barracudas. At first I though it was the mag until I tried JSBs. They fit perfectly, so the issue was the ammo/mag combination. Did you find a similar issue or did your problem persist with different brands and types of ammo?

You have to be real careful on the rifled (barrel) side. One of the burrs was so bad that it chipped off a piece of material from the magazine when I tried to gently polish it by hand with some 600-grit wet/dry sand paper.

So I went in there using some of that dark grey 3M polishing cloth (Tri-M-ite) wrapped around a .17cal nylon bristled brush, attached to a custom rod that I made for my lathe. You could probably use a variable speed drill, but it's important to go straight in and slow at first. I have a milling attachment that I can attach to my my tool post to hold the magazine in place (real pain in the a$$ to setup though). I worked each chamber with that grey and then hit them with olive green color polishing paper.

For the no-rifled side of the mag (loading side), I just went in with a high quality green 600-grit rubber bit, which was fairly quick and easy. I would not use one of those types of bits on the rifled side! It's too abrasive and could destroy the mag chambers.

 

[mtnGhost]

@mtnghost Nice looking rifle and great post! Thanks for sharing. I don’t think I’d have thought to look for burs or chamfering in the mag. What did you use to polish it?

@randy_68 I’ve had a similar issue with pellets scraping the magazine (front and back) while loading and indexing to the next chamber. This occurred in a .25 Brocock/Daystate Mag with H&N Barracudas. At first I though it was the mag until I tried JSBs. They fit perfectly, so the issue was the ammo/mag combination. Did you find a similar issue or did your problem persist with different brands and types of ammo?

You have to be real careful on the rifled (barrel) side. One of the burrs was so bad that it chipped off a piece of material from the magazine when I tried to gently polish it by hand with some 600-grit wet/dry sand paper.

So I went in there using some of that dark grey 3M polishing cloth (Tri-M-ite) wrapped around a .17cal nylon bristled brush, attached to a custom rod that I made for my lathe. You could probably use a variable speed drill, but it's important to go straight in and slow at first. I have a milling attachment that I can attach to my my tool post to hold the magazine in place (real pain in the a$$ to setup though). I worked each chamber with that grey and then hit them with olive green color polishing paper.

For the no-rifled side of the mag (loading side), I just went in with a high quality green 600-grit rubber bit, which was fairly quick and easy. I would not use one of those types of bits on the rifled side! It's too abrasive and could destroy the mag chambers.

I also wound up re-crowning this barrel. My dial test indicator showed that the rifling was slightly uneven, so I shortened the barrel slightly and put a 45 degree crown on it.

 

[mtnGhost]

Short video of how it groups now. Unfortunately the winds were pretty vicious yesterday, and I didn't lean harder on the velocity (most accurate at ~1075 like I mentioned), but they look promising:

https://m.youtube.com/watch?v=BkEikRCjD1U&feature=youtu.be