Help! Need more power from my Gamo Urban

Forums PCP Airguns Help! Need more power from my Gamo Urban

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    Slash91
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    I am about 1.5 years into my journey down into the airgun rabbit hole. I recently sold my Marauder .25 and replaced it with a Gamo Urban. 22. Before anyone comments about how foolish that was please allow me to explain my motives. I found the mrod to be way too heavy and loud for my purposes. I also did not care for the feel of the synthetic stock, how it is flat instead of rounded on the front/bottom. 

    So, the Urban is light, easy to hand pump, and feels great in MY hands. And I have found it to be accurate with any pellet I feed it. I am very happy with it. Except, I want more POWER. And I have no idea how to find it. 

    That’s why I am posting here. Any thoughts? 

    Thanks. Chris 

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    mikebeggs
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    Hi Chris,

    I have an Urban and have done a lot of experimenting …Have you tried to adjust the hammer spring tension? Also I would recommend installing a regulator, then you can adjust accordingly…There are limits to what you can do without adjusting plenum volume, changing hammer spring and resizing the transfer port…

    I have mine with a Alteros Regulator, but would probably do a Huma Next time around, if you set the regulator pressure higher and adjust the hammer spring all the way in, you can increase power but as I said with limits…I prefer my gun shooting around 820 fps with 14.35 JSB, more accurate and good out to 50 yards…

    Hope this helps
     

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    Slash91
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    Ok. So, I understand the hammer spring tension adjustment generally. But, specifically, how does one do that?
    I recall buying a heavier spring for my Benjamin Maximus and that was an easy swap. 

    Also, how difficult is it to install the Huma regulator? I am no stranger to a screwdriver, but I am also no gunsmith, either.

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    Eaglebeak
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    You should be able to wind the hammer spring preload in a couple of turns and perhaps, open up the transfer port a little. Other than that, there isn’t much you can do without modified springs and hammer weights. The hammer spring adjustment is located behind the plastic end cap on the back of the air tube. Clockwise will increase the preload. Forget about using a regulator. You will only get fewer shots and less power with the stock tune.

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    prfssrlee
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    Hi Chris, I just learned how to adjust the hammer spring pre-load by turning a screw inside a slide-off plastic end cap behind the hammer spring. You access the screw by removing the gun from the stock (take out both screws labeled #32 on the diagram below). On the diagram, part number 17 is called the “cylinder end cap”. The Urban has a slightly different shaped piece, but that’s the one to remove – it just slides straight back. The cylinder that this end cap fits into on the diagram holds the allen head screw that you turn to adjust pre-tension on the hammer spring.  CW for more tension (ie, more power) and CCW for less tension – but don’t start by turning it CW, start by turning it CCW all the way so you have a refence point. That screw has 15 turns of adjustment but comes from the factory somewhere near the higher power end. The allen wrench you need is 4mm.

    So insert the allen wrench and turn that screw all the way CCW until it doesn’t turn anymore – that is fully retracted and the lowest power possible (at least by this adjustment). Now turn that screw 15 turns CW and you’ll be at the max power setting. If you go to higher power first, there is nothing to stop the screw from going off its threads and you don’t know where you are starting from.

    At max power, my Urban gives me 28 fpe when firing H&N Predator Polymag Shorts (15.89gr) – so I guess it would give me about 30 fpe if I used something heavier like 18.19gr JSBs. Beyond this simple adjustment, I’d refer you to one of the many more experienced Urban AG owners on this forum and on gta. They are very willing to share advice and suggestions. Good luck!

    (oops – just saw someone posted this same advice – maybe this diagram is helpful to you)

     

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    Mattblum
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    I too have an Urban. I only have about 20 yards to shoot in, so it’s more than powerful enough. My main concern is even shot strings. You can get a huma for the coyote that will also work on an Urban. I’m going to do that. Can’t afford the gun I really want, so I’m going to soup up the one I’ve got. Need a crony soon too. Can’t really tune an airgun without one as far as I can tell.

    Let us know how it goes!

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    mikebeggs
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    Regulator is easy if it’s an Alteros which I have just slips into the airtube. Huma is more complicated but Huma has very good and easy to follow pdf instructions for the BSA Buccaneer / Gamo Urban on its website…I get 40 good regulated shots on the regulator before I fill up, drops off just after that, consistency and accuracy is improved by regulating, I can get the following groups…First one is 25 meters JSB 14.35, Second is a 10 shot group 35 yards… Third is a 10 shot group 35 yards.

    Gu is more predictable now its regulated…

    10 shots 35 yards

    10 shots 35 yards

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    Eaglebeak
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    “mikebeggs”Regulator is easy if it’s an Alteros which I have just slips into the airtube. Huma is more complicated but Huma has very good and easy to follow pdf instructions for the BSA Buccaneer / Gamo Urban on its website…I get 40 good regulated shots on the regulator before I fill up, drops off just after that, consistency and accuracy is improved by regulating, I can get the following groups…First one is 25 meters JSB 14.35, Second is a 10 shot group 35 yards… Third is a 10 shot group 35 yards.
    Gu is more predictable now its regulated…

    10 shots 35 yards

    10 shots 35 yards

    
Have you run a string over the chrono? Slash91 is looking for more power. I tried the Altaros reg in my BSA Buccaneer and it flattened the power curve at the bottom not the top. It also decreased my shot count by 20%. I tried several pressure settings but even in the tip of the guns sweet spot about 165-170 bar I was still losing 20-30 fps with the 15.9 JSBs. It is not possible to get more power by adding a reg in any gun aspecially one that is not designed for it. Any power or shot count gains come from the tuning. All the reg does is equalise the pressure for each shot until the set pressure is reached. In the case of the Gamo Urban, It has a smaller air tube than the Buccaneer and Coyote so the plenum in the reg is going to take an even larger % of the very small air chamber. Less air = less shots or less power. In my case it was both. My reg is the same as yours. I’m guessing if you are getting 40 regulated shots, your powerwill be no more than about 15 FP. Sorry to rain on your party.

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    Slash91
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    Great stuff, gents. Keep it coming.
    Plan on doing the spring adjustment and the trigger adjustment this weekend. 
    As another stated, I really want a different gun, but 1200 is a lot of cash, so going to make the most of this one. 
    £
    Thanks to all!

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    mikebeggs
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    Eaglebeek, your assumptions are correct…I had the same problem when I first installed the Alteros Reg, lower shot count, I took it out 6 or 7 times to play with the settings the combination I have now – These shots where taken with a lower reg setting and backed out hammer spring tension that gives me around 750 -760 fps gives me around 17 FPE, but great accuracy…However I prefer to hunt at a little hotter and now have the hammer spring tension a little further in to raise FPE to 815-820 with JSB 14.35 .My gun is tuned for short to mid distance accuracy not power…40 shots is now routine…It also took a while for the regulator to settle in…It was at times very frustrating and I almost binned the regulator, even pulled it apart, change o-rings, spoke to the factory… next time I will probably do the Huma….Everything is give and take and as posted above to slash in my first post:

    “I have an Urban and have done a lot of experimenting …Have you tried to adjust the hammer spring tension? Also I would recommend installing a regulator, then you can adjust accordingly…There are limits to what you can do without adjusting plenum volume, changing hammer spring and resizing the transfer port…”

    Just sharing my experience with the Urban, some need power, some accuracy, accuracy in my book trumps power, but each unto their own…

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    mikebeggs
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    Why I recommend the Huma, is that they seem to be garnering a lot of mainstream brands including them into production lines, the other is that part of the Huma Regulator installation is to drill and enlarge the transfer port to 4 – 4.2 mm, I have not done this but would be interested to hear from anyone that has…

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    Eaglebeak
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    mikebeggs, You have a better understanding of your gun than I gave you credit for. My buccaneer, unregulated, with two turns clockwise on the hst gets 30 shots from a 230 bar fill. With the 15.9 JSBs, it starts at about 905 fps and climbs to about 925 between 170-160 bar and drops back to about 905 again at about 135 bar. With the reg set at 160 bar I only get 18 shots between 900 and 910. Backing off the hst only decreases power so it isn’t wasting air. Accuracy at 925 fps at 30 yards is 5 shots inside a .35 hole. Like you said the reg is good if you want to tune for less power and more consistent spread but as you can see, the valves on these guns do a pretty good job unregulated. In my case, there are no accuracy gains in tuning down. That is why don’t bother with the reg in this rifle. Anybody who thinks they can raise their power by adding a regulator is barking up the wrong tree.

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    mikebeggs
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    Agreed, every design has its limitations…but love the gun, especially for $290…

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    Slash91
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    “So insert the allen wrench and turn that screw all the way CCW until it doesn’t turn anymore – that is fully retracted and the lowest power possible (at least by this adjustment). Now turn that screw 15 turns CW and you’ll be at the max power setting. If you go to higher power first, there is nothing to stop the screw from going off its threads and you don’t know where you are starting from.”

    @prfssrlee

    Thank  you. Is it possible to turn that screw too far when going CCW such that the screw falls out and cannot be easily replaced? 

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    mikebeggs
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    I found that mine reached a dead stop when all the way in, but I have read from others that you have to be careful to not overtighten it otherwise it could run out of thread…
    I have not had that problem, mine stops at full in position but I am gente towards the last few roatations…I have stripped the gun down to individual pieces on many occasions and am confident that if it came off that it can put back on :)

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    prfssrlee
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    @Slash91- the threads just stop, so as long as you don’t force it CCW, you’ll be fine. Mine came at about 12 turns in – so pretty close to full power. 

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    Eaglebeak
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    In my case with the Buccaneer, I just started at the factory setting and turned it in clockwise 1/2 turn at a time and tested the results. I found that any more than 2.5 full turns affected accuracy and efficiency noticeably. Your Urban will be tuned a little differently but doing this should be safe to do and not risk running out of thread. 2.5 turns in to give me a peak of just over 930 FPS with the 15.9 JSBs. I settled on about 2 full turns. Just remember to record any changes so you don’t lose your starting point.

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    Slash91
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    Do I need to de gas the air cylinder prior to removing stock and making this adjustment?  Recall, I am new to this. 

     

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    Eaglebeak
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    “Slash91”Do I need to de gas the air cylinder prior to removing stock and making this adjustment?  Recall, I am new to this. 
     

    
  No, not necessary.

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    Slash91
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    Thanks, Eaglebeak.

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