Tuning Kral Jumbo pressure questions

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Dr. Kralenstein

Dr. Kralenstein

Member
Apr 14, 2022
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The Laboratory, United States
I'm wanting to raise the fill pressure from 2900 to around 3500 if possible. Wanting to get more shots and power when I upgrade the springs. I know they have a 3000 psi burst disc which I can swap out for a higher one. I'm just wondering if the standard 425cc bottle will handle the higher pressure. It's not stamped anywhere on the bottles fill rating, just the laser engraving by kral saying fill to 2900 psi/200 bar. 

These guns will valve lock around 3300 psi is what I've read, but I'm sure the velocity is low until it gets closer to its set fill pressure. I've ported everything out to 3/16" and with the 16" 25 caliber barrel I'm getting around 830-840 fps with AAs 25.4s.

Would like to see 900 or more with some spring work and higher pressure. Trying to avoid getting a regulator since it pushes the bottle out further than I'd like. I'm willing to get a 500cc bottle, just don't know what brand to get that's truly rated to 4500 psi. I see a bunch of cheap ones on ebay for 50-60 bucks, but I doubt their quality. 
 
More shots OR more power. Pick one and work towards that. There is only so much you can do with two variables. Your gun will have a sweet spot where it is most accurate. My humble suggestion is to shoot for accuracy rather than absolute power.

FWIW my Kral has about 110 shots with a very good plateau for 60+ shots. SD of 1 and ES of 8 for those 60 shots. Don't really care how fast exactly it is shooting, when each shot overlaps the last shot 
 
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My jumbo stacks pellets currently, I just want it up to about 45 fpe with this barrel length. I have a full length rifle barrel for it also which will hit my goals, but trying for that number with the NP-03 barrel thats on there currently. 

If I get the 500cc bottle and up the pressure, I will get more shots than the 425cc plus the higher pressure would get me the power. It currently gets 40 shots in its power curve, if I could get 50 shots at 900 fps with the 16 inch barrel I'd be happy. 


 
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These guns are pretty robust compared to say a benjamin discovery/maximus which I've taken up to 3500 psi before. Those are tube guns with all the parts inline so you rely solely on valve screws to hold everything. The kral guns are self contained valve/tube design. 

I'm not saying I'm going yo to 4500 psi lol. I've read posts were some of these guns, like puncher breakers and other jumbos, have been pushed to 3600 psi with stock parts. The action blocks are stout on these rifles. 

In my experience with tuning pcp rifles for more pressure, as long as things are upgraded like valve screws(which the kral doesn't have, it's just end caps and o-rings), an extra 500 psi isn't asking too much. The design of these guns makes me think it'll handle it, especially if I upgrade to a bottle that can handle 4500 psi and I run only 3500 psi. Lighten the valve spring and stiffen the hammer should result in allowing the valve to open under the higher pressure. That would get me more power at around the amount of shots. If the porting were restricted, but the pressure raised and springs upgraded, it would add shot count. I've done this multiple times on the discovery style rifles. Usually with great results. In theory, it should work on this setup.
 
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Whatever it's your life I don't think its a great idea if u know then why did u ask ?
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You're a pleasant person to be around I'm sure. These comments are the reason I don't post on this forum much. 

I'm asking because I was hoping someone on here may have went down the same road I'm trying with this particular platform. Troy Hammer comes to mind. I know he has done higher pressure builds on these guns, without all the high dollar tricks and regulators etc.
 
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When you say these guns are stout, are you speaking from appearance, or from a metallurgist standpoint? My Kral looks robust, but it feels soft when I work on it (machining) compared to other guns I own. So seeing how I’m not a metallurgist, I error on the side of caution. 



I agree on being cautious, but think of it like this. You know this jumbo inside and out.

The hammer hits the valve, the air goes up thru the transfer port hole, into the barrel. Not much to it really. If anything were to fail, it would be an o-ring I would imagine. The receiver block is pretty thick aluminum, and we're talking 3500 psi, not 30000 like some aluminum firearms see. An AR15 comes to mind. Sure the bolt carrier and barrel/battery are forged steel, but they operate inside a thin piece of aluminum. Those operating pressures are pretty high in those rifles. Apples to oranges I know, but I guess my idea on it would be some form of safety margin from the manufacturer. I doubt they would build the rifle for 3000 psi, but have it blow into pieces at 3100 psi lol. Most build with a 3:1 safety margin.
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Not telling anyone to do this, I know how we are with liability. I fill my NP03 to 3,500 everytime I air her up. It’s regged so I don’t have valve lock issues, but the tube seems just fine. I know you can have metal fatigue over time from doing this, don’t know how much 600 psi is going to contribute. I know of a few that do this and have been for a while, haven’t heard of any failures.

Beau
 
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Yes, going a little over definitely should not pose a problem. I have one gun that I fill to 265b only when I take it hunting because I need the extra 15b to give me exactly 2 mags. But taking a 200b gun and making it a routinely filled 250b gun is not something the manufacturer decided to do when they were programming their laser engraver so it could be a couple things. The one reason that will green light your needs is they say fill to 200b because that’s where their porting and hammer spring are designed to function best since it’s unregulated. They could put 250b on the gun but customers would have to fire 80 shots at almost valve lock to get down to the guns components happy operating range. Guess you would have to call Joe Kral to get the real reason. 
 
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This is exactly what I was getting at. It would just experience valve lock if I didn't change any springs. Every pcp I've owned will valve lock when filled above their listed fill pressures. I've had guns arrive overfill and they didn't explode lol. I just had to bleed off the pressure til it got to where it would open the valve properly.

If you ask me, most guns come over sprung in the hammer anyways and could use a but more psi to even things out. The issue with overfilling these guns is they have a 3000 psi burst disc. 


 
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Sorry I was just telling u my opinion and when dealing with hpa I don't want any one to have a accident or worse I have pushed marauders to 3200 and discos to 3000 with the correct screws I have not messed with kral you may be able to reach higher speeds with lighter spring in the valve and a heavier hammer spring peek poppets also help you can probably push it aways but I don't know what the safety margins are on the kral again sorry for being mean just reminded me of a different old member that was way over filling and wouldn't listen to anyone about it he was pushing a tube gun rated to 3000 up to 4500 -5000 psi and tried to say it was safe 
 
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Sorry I was just telling u my opinion and when dealing with hpa I don't want any one to have a accident or worse I have pushed marauders to 3200 and discos to 3000 with the correct screws I have not messed with kral you may be able to reach higher speeds with lighter spring in the valve and a heavier hammer spring peek poppets also help you can probably push it aways but I don't know what the safety margins are on the kral again sorry for being mean just reminded me of a different old member that was way over filling and wouldn't listen to anyone about it he was pushing a tube gun rated to 3000 up to 4500 -5000 psi and tried to say it was safe 



It's all good, I appreciate the worry about being safe. No hard feelings or anything, just came across like "wow this is my like 13th post and I'm already here" lol. 



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Now on to the burst disc discussion. That is a safety mechanism. I will not swap out a burst disc for a higher one. They are definitely telling you they don’t want to see that component seeing a higher pressure.
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Well if I'm wanting to go up to 3500 psi, and the burst disc fails at 3000 psi, that's a dilemma. I thought about removing it and plugging the hole with a pipe plug, but now I'm asking for an onslaught of "you're an idiot" posts lol. 
 
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Yes, after all it’s just a pellet gun. A toy for the most part. If you compare let’s say a 4,000psi bottle reg with the appropriate burst disc to a 3,000psi bottle reg, there are differences. There are 4 threads instead of 3 where it screws into the breech. So why do they feel the need to warn customers about some things but absolutely shut down the operation when they install burst discs. That’s guidelines versus dropping the hammer. How you proceed and just how important achieving a goal with your toy is ultimately up to you. 
 
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