Mounting Holosun 507c Reflex Sight on Huben GK1 - Sight In (Issues and Resolution)

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Ezana4CE

Ezana4CE

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Jan 15, 2021
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Mounted and attempted to sight in my reflex sight. I started at 10 yards Shooting .25 GK1 V3 with the Holosun 507c mounted using a ReddotMate mounting plate. I shot JSB King Diabolo pellets, 24.39 grains I believe. Anyhow, I seem to have run out of elevation before getting the center dot aligned with my POA The best I got was consistent POI hits about 0.5” - 1” low. Doe anyone have any suggestions on how to get past this hurdle and improve my sight in process with the GK1?

IMG_8840.jpeg
 
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Bummer! Initial thought is optic height is too high. I didn't have any problem sighting in my Hawke Frontier Reflex Dot at 15y (with the picatinny adapter underneath it). I'm unaware of any low profile adapter with MOA built in. It may just be a limitation of the adjustment offered by Holosun.

Are you using a picatinny to dovetail adapter? If so you could possibly try to place a shim between the adapter and the dovetail rail.
 
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@Michael The only adapter I used is for the mounting plate to affix the adapter to the hole that was used to adjust the elevation with the stock rear sight.you can see the plate between the reflex sight and the top of the receiver in the photo.

As for the reflex sight, the manual says that it has 50 MOA worth of adjustment. I counted 41 clicks “up” before I started feeling resistance in the elevation screw. Consequently, my shots still fell 0.5” - 1” low consistently while standing at 10 yards.
 
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Ezana4CE said:
@Michael The only adapter I used is for the mounting plate to affix the adapter to the hole that was used to adjust the elevation with the stock rear sight.you can see the plate between the reflex sight and the top of the receiver in the photo.

As for the reflex sight, the manual says that it has 50 MOA worth of adjustment. I counted 41 clicks “up” before I started feeling resistance in the elevation screw. Consequently, my shots still fell 0.5” - 1” low consistently while standing at 10 yards.
Click to expand...
Hmmm, shimming that probably won't work. Have you tried to sight it in a bit further, say 15y?
 
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I'm an air gun noob. But not a pistol or optic noob.

I don't know this gun. And everything's black and lots of shadows. So, I can't tell how it's mounted. But my eyes see a difference in the plane of the base of the optic and the barrel axis. It may be optical illusion due to the all-black / shadows thing going on. But I've drawn this (perhaps exaggerated a bit on the top line) to demonstrate what I think I'm seeing. But if that was the case, you'd more likely be shooting HIGH. So, I'm not sure what's going on.

1748631680538.png



I have a couple of Holosun 507c optics on my bang-bang pistols. :cool: Love'em!
 
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Racer88 said:
I'm an air gun noob. But not a pistol or optic noob.

I don't know this gun. And everything's black and lots of shadows. So, I can't tell how it's mounted. But my eyes see a difference in the plane of the base of the optic and the barrel axis. It may be optical illusion due to the all-black / shadows thing going on. But I've drawn this (perhaps exaggerated a bit on the top line) to demonstrate what I think I'm seeing. But if that was the case, you'd more likely be shooting HIGH. So, I'm not sure what's going on.

View attachment 566289


I have a couple of Holosun 507c optics on my bang-bang pistols. :cool: Love'em!
Click to expand...
@Racer88 It's hard to see the barrel alignment because the gun has a shroud and moderator adapter at the crown that cover the barrel. Consequently, none of the barrel is visible in the photo. In addition, the bottom red line isn't flowing the shroud in a straight line.

I may have figured something out. I'll investigate it this weekend and post what I find if my hunch reveals anything that remedies the issue.
 
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Ezana4CE said:
@Racer88 It's hard to see the barrel alignment because the gun has a shroud and moderator adapter at the crown that cover the barrel. Consequently, none of the barrel is visible in the photo. In addition, the bottom red line isn't flowing the shroud in a straight line.

I may have figured something out. I'll investigate it this weekend and post what I find if my hunch reveals anything that remedies the issue.
Click to expand...

Yep... admittedly, I was guessing. And I realized that the photo may not really reveal the alignment. Could be an "optical illusion." Plus, if it WAS correct, you'd be shooting high, not low. Soooooooo.... Let us know what you find out!
 
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I had this problem. One solution requires a very thin wedge. I printed one. It might have been either 1 degree or 1/2 degreeb(don't remember). I basically copied the RMR foot print. It worked well enough. However, the culprit is insufficient adjustment of the Holosun sight to handle short vs long range and high sightline vs the barrel. So my wedge worked for shorter range but not longer. I'd guess you'd pick the range you want to shoot at and make a wedge that would have the optics centered in the elevation adjustment range?
 
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WobblyHand said:
I had this problem. One solution requires a very thin wedge. I printed one. It might have been either 1 degree or 1/2 degreeb(don't remember). I basically copied the RMR foot print. It worked well enough. However, the culprit is insufficient adjustment of the Holosun sight to handle short vs long range and high sightline vs the barrel. So my wedge worked for shorter range but not longer. I'd guess you'd pick the range you want to shoot at and make a wedge that would have the optics centered in the elevation adjustment range?
Click to expand...
@WobblyHand I will take this into consideration when I go to troubleshoot the issue.
 
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I'm using the same sight on the GK1 and didn’t have an issue with installation and sight-in. Though I don't remember how far the range of adjustment went before sight in distance with mine, it was fairly close when first installed and sighted in at 10 yds. At 10 yards, the barrel, shroud, and reflex sight should all be relatively flat with factory machining, so it leads me to believe something internally may be bound up or out of place somewhere. Holosun has a pretty good warranty and will likely just swap it out if you contact them.

Another thing to investigate, something that I discovered that was throwing my shots with the GK1 moderator, was pellet clipping because the moderator didn't sit flush when tightened. The inside of the shroud made the moderator kick sideways when snuggled up. Here's the write-up and fix on it. (Page 2, Post 32)

Huben - Any issues or problems with Huben gk1 please share your experience

As a follow-up to this, I finally was able to contact the Huben factory yesterday of this issue and I have received an acknowledgement. We will see what, if anything this brings.. I received a reply from the factory> > > see below: Dear Steve, Thanks for choosing Huben GK1! Thank you very...
www.airgunnation.com www.airgunnation.com
 
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Airgun-hobbyist said:
I'm using the same sight on the GK1 and didn’t have an issue with installation and sight-in. Though I don't remember how far the range of adjustment went before sight in distance with mine, it was fairly close when first installed and sighted in at 10 yds. At 10 yards, the barrel, shroud, and reflex sight should all be relatively flat with factory machining, so it leads me to believe something internally may be bound up or out of place somewhere. Holosun has a pretty good warranty and will likely just swap it out if you contact them.

Another thing to investigate, something that I discovered that was throwing my shots with the GK1 moderator, was pellet clipping because the moderator didn't sit flush when tightened. The inside of the shroud made the moderator kick sideways when snuggled up. Here's the write-up and fix on it. (Page 2, Post 32)

Huben - Any issues or problems with Huben gk1 please share your experience

As a follow-up to this, I finally was able to contact the Huben factory yesterday of this issue and I have received an acknowledgement. We will see what, if anything this brings.. I received a reply from the factory> > > see below: Dear Steve, Thanks for choosing Huben GK1! Thank you very...
www.airgunnation.com www.airgunnation.com
Click to expand...
@Airgun-hobbyist I’m haven’t used a moderator with this sight. What sort of mounting base are you using on your Holosun reflex sight?


I used one of these.
IMG_8893.jpeg

www.reddotmate.com

Red Dot Mount Plate For Huben GK1 Optic Mount | ReddotMate

Red Dot Mount Plate For Huben GK1 Optic Mount Must remove the pin of the rear sight (recommended to buy Pin Punch Tools) and take off the rear sight,
www.reddotmate.com www.reddotmate.com
 
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Ezana4CE said:
@Michael The only adapter I used is for the mounting plate to affix the adapter to the hole that was used to adjust the elevation with the stock rear sight.you can see the plate between the reflex sight and the top of the receiver in the photo.

As for the reflex sight, the manual says that it has 50 MOA worth of adjustment. I counted 41 clicks “up” before I started feeling resistance in the elevation screw. Consequently, my shots still fell 0.5” - 1” low consistently while standing at 10 yards.
Click to expand...
The 50 MOA range is from the center, so that's approximately 25 up and 25 down. I believe the Holosuns have 1 MOA click adjustments. So at 10 yards, your 41 clicks should have changed your point of impact 4 inches up. Does that sound about right?

I'm not sure if you did this, but one simple and free trick you can try, if you point of impact isn't corresponding with your adjustments is to turn your elevation screw back several clicks and then turn it back up. Sometimes the mechanism can get stuck. This helps to break it free.

Good luck.
 
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WobblyHand said:
Getting back to this, I used a 1/2 degree wedge. I put an extra set of holes in it so the wedge can either raise or lower an RMR sight. Printed with 0.05mm layers, it takes 11 minutes to print. Maybe someone will find it useful. I printed it with PETG.

View attachment 566649
Click to expand...

@WobblyHand If you have any photos where the wedge is visible while mounted, can you post a couple?
 
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Ezana4CE said:
@WobblyHand If you have any photos where the wedge is visible while mounted, can you post a couple?
Click to expand...
It's kind of funny, the wedge isn't really visible when installed, It's 0.023" thick at the thickest point, and 0.010" thick at the thinnest. Here's a pic of the 1 degree wedge. (Just so the angle is more obvious!)

My Holosun came with an RMR mount. I used the huben3dparts Unimount with RMR. In between the sight and the Unimount I installed the wedge. The holes in the wedge allow the pins to go through, that are required for the sight registration. The wedge is so thin, you don't need to do anything special with the screws, just use what you have.
RMR_1deg_mount_reversible.jpg
As mentioned previously, you need to ensure the screws are not so long that they bottom out in the hole before fully tightening. At least for me, the screws were fine.

To show you it installed with my Holosun, I'd need to take off the sight. I'd rather not do that if I don't have to.
The wedge goes between the sight and the Unimount, right where the line is, just under the HE507C-GR text.
PXL_20250601_005519674.jpg

Hope that helps.
 
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Ezana4CE said:
@Airgun-hobbyist I’m haven’t used a moderator with this sight. What sort of mounting base are you using on your Holosun reflex sight?


I used one of these.
View attachment 566594
www.reddotmate.com

Red Dot Mount Plate For Huben GK1 Optic Mount | ReddotMate

Red Dot Mount Plate For Huben GK1 Optic Mount Must remove the pin of the rear sight (recommended to buy Pin Punch Tools) and take off the rear sight,
www.reddotmate.com www.reddotmate.com
Click to expand...
I have that plate as well as the 3D printed plates for two other red dot base patterns. None gave any issues sighting in with minimal adjustments on three different red dots. Let us know what you figure out with it.
 
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