GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: n2omike on June 05, 2019, 03:07:49 PM
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I bought a Gamo Urban a year or two ago, and it shot amazing. Recently, it started shooting extremely low... as in completely out of the scope adjustment.
I noticed I could see daylight between the bottom of the barrel and the barrel band o-ring.
I loosened the barrel band screw, and moved it forward... and noticed the barrel sprung upwards.
There are two receiver screws on the front that hold the receiver to the air tube. I removed them. Receiver does not come off like a Marauder unless I need to pull harder, but there are just the two of them on the front. None on the top of the receiver in the rear.
Here is where it gets weird...
When I tighten those front receiver screws, the barrel springs up pretty hard. If I loosen them, and just hold the front of the receiver down with my hand, the barrel centers itself in the barrel band perfectly. Tighten those two screws on the top, and it springs back up.
I believe the screws are behind the transfer port, or something else connecting the barrel to the air tube, and when tightened, the lever the front of the barrel upwards. I don't know if it would be swollen TP o-rings, or something else that may be holding things up there.
I found a diagram, but am not sure how to take this gun apart to see what's going on. Does anyone have some insight or pointers??? Below is a link to an exploded Gamo Urban diagram. I've worked on and modified all of my Benjamin Marauders, but had pretty good instructions. I just don't want to break anything.
https://spares.bagnallandkirkwood.co.uk/wp-content/uploads/2016/04/GAM3-Exploded-Diagram.pdf
Thanks!
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Minor update...
Found the hidden receiver screw in the back of the trigger group. After removing that, the receiver comes free of the air tube.
Also figured out that the transfer port gaskets are the same size as a .25 Marauder barrel O-ring.
Factory o-rings were torn and had shards hanging from them. Not sure if it was affecting the seal. Gamo TP is much beefier and robust than the Marauder. Stock Transfer Port ID is 0.0158"... and using a .25 Marauder barrel sized o-ring, has a lot of room to grow. Will assemble and see what happens...
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Thing is getting annoying...
I flipped the barrel 180 degrees and removed the Transfer Port all together... and the barrel still springs upward as it is tightened.
Also figured out that the .25 Marauder barrel o-ring is just a little on the thick side. A found an R04 o-ring in a generic kit that matched up better.
Seems like I should be able to see it, but it's eluding me so far...
Back at it...
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Don't have anything to add but filling along as I am thinking of getting one of these, thank you
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Same here. Nothing to add but I have a urban also so will be watching this thread. Hope you find the problem.
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If you hold the receiver to the air tube with carpenter clamps, the barrel is perfectly centered. But as you tighten the front receiver screws, you can watch the barrel rise in the barrel band. Having a hard time putting a finger on it...
Then the barrel band pulls down on the barrel, and the gun shoots so low that you have to put shims under the rear of the scope to get enough scope adjustment.
It didn't use to do this... and now it does. That's the weird part.
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Does it do that without the TP installed?
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Does it do that without the TP installed?
Does it with no TP, does it no matter what you do. Even removed the barrel and installed it upside down with no TP to see if it was bent or something... Same thing. Sanded a little off the ends of the TP to see if it was bottoming out and causing things. Same thing.
As the receiver flattens out as the front screws are tightened, the barrel starts pointing north, and gets caught by the barrel band. I'm not brave enough to remove the barrel band, as my 13 year old son is the primary shooter... and 13 year old boys can use something securing the front of the barrel... as they are generally more adventurous than graceful. lol
Finally threw in the towel, put 0.030" worth of brass shims under the scope in the back, and called it DONE. I've had enough of it.
Seems to shoot fine. Just don't know what happened to cause it. I did remove the barrel band o-ring to give the barrel a little more room. Might put it back, depending upon how it groups. We'll see.
It's been a good gun, and likely still is. It's just primarily used by a 13 year old boy... so who knows what happened. I couldn't figure it out.
Thought I'd edit this post to show a place that sells some Gamo Urban parts. Also has an exploded parts diagram. Also kind of bookmarking it on here in case I need to find it in the future. lol It's where I got the parts diagram linked to in my initial post. Eh, another edit... Noticed it's European. I'll leave it there, anyway... lol
https://spares.bagnallandkirkwood.co.uk/gamo/gamo-phox-airgiun-spare-parts/ (https://spares.bagnallandkirkwood.co.uk/gamo/gamo-phox-airgiun-spare-parts/)
Here's a disassembly video... It's in Spanish, but you can probably still figure it out. lol
https://www.youtube.com/watch?v=_IdDJUatBgA (https://www.youtube.com/watch?v=_IdDJUatBgA)
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That's why I cut off my barrel band. If it's good enough for BSA to leave off the barrel band, and this ismade by BSA, then... Plenty rugged without. Mine pulled the barrel down a quite a bit. I would like to find out the Oring sizes for the fill block and internals!
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That's why I cut off my barrel band. If it's good enough for BSA to leave off the barrel band, and this ismade by BSA, then... Plenty rugged without. Mine pulled the barrel down a quite a bit. I would like to find out the Oring sizes for the fill block and internals!
Same here. No barrel band on my Urban, and poi never wanders.
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yep no barrel band on my .177 and .22 Buccaneers do still have it on my Urban but have not dissembled them at all yet... can pull and put back on the band on the Buccs because they are pre big can on the end and the muzzles are threaded...
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Oh, also with my .177 Buccaneer removing the barrel band improved accuracy... on my .22 it does not seem to mind the band but is off so I can have a partial shroud...
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JUst to mention a couple of odd things that have happened...not that they evidently are common.
One Hatsan never could get it's breech to fit flat to the tube. TP or no TP, it was lifting one end or the other (depending on how it was tightened). I "cheated" and never really did the work to fix it "right" (layout blue..spotting it in...hitting the high points...repeat/repeat/repeat). With the barrel into the reciever, figured out it was most in line with the air tube with the front tight and the rear attaching screw just snug. So I just shimmed the rear of the receiver until I could tighten all the screws tight and left it alone (and it still shoots well years later).
HAve pulled barrles and rolled them across a real flat surface (OK..not like lab-grade flat...more like plate glass flat) and found the barrels to be cock eyed. Likely not your problem as you've rotated the barrel.
Retention screws that directly touch the barrel (like most of them) are subjecxt to the "slack" tolerances of the fit of the barrel to the receiver.The ones with o-rings give the illusion of tightness,but the o-rings can be compressed by the screws unevenly.
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JUst to mention a couple of odd things that have happened...not that they evidently are common.
One Hatsan never could get it's breech to fit flat to the tube. TP or no TP, it was lifting one end or the other (depending on how it was tightened). I "cheated" and never really did the work to fix it "right" (layout blue..spotting it in...hitting the high points...repeat/repeat/repeat). With the barrel into the reciever, figured out it was most in line with the air tube with the front tight and the rear attaching screw just snug. So I just shimmed the rear of the receiver until I could tighten all the screws tight and left it alone (and it still shoots well years later).
HAve pulled barrles and rolled them across a real flat surface (OK..not like lab-grade flat...more like plate glass flat) and found the barrels to be cock eyed. Likely not your problem as you've rotated the barrel.
Retention screws that directly touch the barrel (like most of them) are subjecxt to the "slack" tolerances of the fit of the barrel to the receiver.The ones with o-rings give the illusion of tightness,but the o-rings can be compressed by the screws unevenly.
Thanks for the info!
As for shimming... I tried that. As the front screws are tightened, the barrel rises and hits the top of the barrel band... but the gun still shoots LOW. Shimming to keep the barrel centered just makes it shoot even lower. (have thee 0.010" brass shims in rear of scope just to get in its adjustment range) I think I need to remove the barrel band completely, and allow it to rise to where it wants to go. It just makes me nervous because my son is a 13 year old boy... and it provides protection from falls and leaning on stuff. lol
The barrel retention screws are grub screws. No o-rings... just grub screws tightening against flats machined onto the barrel. Barrel is straight. Seems like a fairly simple design... once I found the hidden, captured receiver screw down in the rear of the trigger group.
As for barrel bands... On my Marauders, I took some 1/8" foam that was sticky on one side... and lined the barrel part of the band with it. Works great for POI issues... as it fills the void pretty much perfectly, and the barrel is already nice and centered. Works a lot better than all the other aftermarket bands they came out with. Cheaper as well. I would like to have some similar protection up front for the Gamo to guard against mishaps, but the barrel alignment within the band is terrible. It USE to be fine... but, I don't know what happened... but, maybe freeing the barrel from the air tube might be required. Just makes me nervous. Maybe I can fabricate some other kind of guard for the front... maybe just cut the very top off the band, and leave the sides to guard it. Hmmmm... :)
Wow, guess you can't say c r a p on this forum. lol
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My Urban took a spill off my rifle rest sans barrel band. It bounced off the table and fell about 3 feet to the ground. I picked it up wiped it off and continued shooting with no shift at all.
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the Huma instructions show pretty much all you need to understand the urban. I used them to install my regulator, but it shows the OEM parts.
http://foto.huma-air.com/foto/installation%20guide%20BSA%20Buccaneer%20Gamo%20Coyote.pdf (http://foto.huma-air.com/foto/installation%20guide%20BSA%20Buccaneer%20Gamo%20Coyote.pdf)
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I can answer any questions you may have about the Gamo Urban. Best regards. F.A.
Update videos to come VERY soon.
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I went through the same thing. I did not want to remove the barrel band………I removed the barrel band, and all is well, no more shifting poi, and very accurate and consistent now. I added two large o-rings to fill the space of the missing band on the air tube.
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The problem you're having is due to the tube not being straight. Notches and slots
are typically punched out rather than formed by milling. A loose fitting die (the piece
that fits inside the tube which prevents collapse) allows the tube to be deformed slightly
and you end up with what I've sketched. Lay a precision straight edge across the
magazine slot, bridging an inch or so either side of it, and you'll notice the gap. The
fix is simple yet a pain in the butt:
determine the measurement "x" (mine required .003"), cut a shim of this thickness
approximately 1/8" by 3/4", curve it to fit across the tube (will help during assembly),
hold in place with a dab of grease.
The same situation exists at the rear where the "hidden screw" holds the trigger block,
though this one isn't as critical.
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remove barrel band add full shroud to protect barrel : https://www.gatewaytoairguns.org/GTA/index.php?topic=152699.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=152699.0)