Hello this is my first post hopeing it's OK just found agn from Googleing I have a kral jumbo in 22 fac model I have fitter a huma reg and drilled ports out to 4.5mm want to work on hammer spring but have no idea what I have to do to upgrade it keep hearing about a Troy hammers beings a genius on kral but I don't no how to Contact him and help on what I need to buy would be massively helpful
Kral jumbo
- Thread starter Pockets1990
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Depending on the age of the rifle it could have 2 different hammers. Only the first Gen Jumbo had the same hammer as the Kral puncher breaker. If it's newer it shares the same hammer with the other bottle guns and needs shortened 8mm and the spring hole drilled to 1/2" the same depth as the stock hole. Then get .48" OD springs 2" Long in .055" and .059" wire diameter from Grainger if in the US. You'll need to make a new spring guide to slip over the factory hammerspring adjuster that is .35" diameter to slip inside the new spring. You can then test the 2 springs to see which gets you to the desired power. Both will be in negative preload so not touching the valvestem even uncocked so it will help with efficiency by limiting hammerbounce.
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This is my first gun I've ever worked on so learning as I go u say to shorten the hammer by 8mm is that the silver part that the spring sits inside? Has a very small flat head screw to it aligned? And take the 8mm of from the side the spring slides into? Sorry if this seems annoying
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You remove the small screw used to align the hammer and it will come out. Yes remove the 8mm from the rear of the hammer where the spring goes then drill or bore that hole to 1/2" and replace the spring with a short stiff spring at or just barely over 2" long and just small enough to slide in the new hole. The ones I use are .055 or .059 wire diameter depending on desired power. I also make a new delrin poppet that is smaller diameter. Factory is typically just over .400" OD and mine are .380" Not sure what you'll have access to. I can get you springs but right now shipping from the US is crazy expensive. With the reg you'll be somewhat limited with the smallish plenum but 30fpe should be obtainable.
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Ideal cheers I'm all ready at at 34ftlbs so just seeing if I can squeeze a bit more out of it thank you very much for your advice and help it's my first high power air rifle as in the UK thiers a lot of red tape to get one and I'm enjoying working on it and seeing the difference u say about the small plenum is thier a better one out thier I have a huma bottle reg currently in and will be buying a 500cc 300bar carbon bottle in the coming months
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I think the Huma reg is only rated to 250 bar regardless of the bottle rating and the valve is only rated to 250bar as well. If your already there you should see a decent increase still without a big air usage difference if any. It's probably the best upgrade you can do for efficiency.
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Yes I'm Aware of the fill pressure but still going from 200 to 250 will be better probably fill to 240 just so it's not on its max all the time
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The huma regulator can have 250 on the bottle side, but at the other side where the air goes to the standard valve the pressure will be between 60-170 bar.(the manometer from the airgun give you the pressure from the regulator).
When the pressure in the unregulated riffle is 250 bar the valve closes very quick the first shots what causes that the velocity is lower the first shots. when the pressure drops the velocity will increase. So you don,t need the 250 bar pressure on the valve in the gun.
You need to search for the sweet spot between regulated pressure and hammerspring tension.
Huma website(We tested the Kral Puncher Jumbo .25 (6.35mm) model, with a regulator output pressure of 140 bar shooting 33 grain pellets at a speed 950 fps. (The regulator output pressure can be set higher) 925 fps for 21 grain slugs and 1030fps with 18.1 grain pellets.) with ,22 you can get probably higher speeds.
Check out this playlist ( ) very informative and going deep in the theory,s , will help you to understand things better.
And this is also interesting about magazines, it is known but a lot of peeps don,t know.
hope this is helpfull
When the pressure in the unregulated riffle is 250 bar the valve closes very quick the first shots what causes that the velocity is lower the first shots. when the pressure drops the velocity will increase. So you don,t need the 250 bar pressure on the valve in the gun.
You need to search for the sweet spot between regulated pressure and hammerspring tension.
Huma website(We tested the Kral Puncher Jumbo .25 (6.35mm) model, with a regulator output pressure of 140 bar shooting 33 grain pellets at a speed 950 fps. (The regulator output pressure can be set higher) 925 fps for 21 grain slugs and 1030fps with 18.1 grain pellets.) with ,22 you can get probably higher speeds.
Check out this playlist (
And this is also interesting about magazines,
hope this is helpfull
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