Increasing hammer spring tension on the Crown

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stoti

stoti

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Apr 6, 2018
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Beautiful Northern California, United States
So I've got my Crown shooting great but I need to max out the hammer spring tension because my regulator is set to 140bar and so I can use the side wheel to make my adjustments when shooting the JSB 33.95's. After I take off the stock, do I turn the allen bolt clockwise or counter clockwise to increase hammer spring tension. I'm assuming clockwise but I found some threads online stating, counter clockwise. That's all I need to know. Thanks, Stoti
 
So check this out... I read the thread at the beginning and have been contemplating the adjustment of my hammer spring tension too, so I did it. There are some very strange results I'm hoping someone can make sense of.

MY Crown's regulator is set at 140bar, power wheel .25-.30, and the hammer spring adjustment set on high. The velocities before adjusting the hammer spring tension were verified by many, many shot strings and averaged as follows: 

JSB 25.4gr. - 940fps.

JSB 33.95gr - 835fps.

After tightening the hammer spring tension about half way, these are the velocities I got:

JSB 25.4gr. - 948fps (average of a 10 shot string) deviation was 11fps and the velocity average went up about 8fps.

Here's where it gets totally whacky...

JSB 33.95gr. - 800fps (average of 11 shot string) the maximum deviation was 47fps. The shot string looked like this: 793fps, 812fps, 812fps, 773fps, 820fps, 785fps, 815fps, 796fps, 790fps, 802fps, 778fps. 

After getting these numbers, I am absolutely stunned and baffled. I don't know how these numbers are even possible or what could cause this kind of shot sting. The velocities decreased over all of the previous shot string averages by 35fps and the velocities are totally up and down with the deviation average of 47fps. SAY WHAT???

I got some good advice from what of the most knowledgeable members of this board who told me to tighten the hammer spring tension all the way and lower the regulator pressure to around 120 and work my way back up. The gun is still super accurate with the 25.4gr. pellets and surprisingly accurate with the 33.95gr pellets too. The inaccuracy with the heavier pellets can totally be attributed to the velocity deviation.

I would really like to hear anybody's thoughts on my situation and hopefully get a dialogue started as to what could be causing one pellet to increase in velocity, have a small average deviation and remain accurate while the other pellet has a decrease in average velocity, and an average deviation of 47fps. 

Please help!!! I'd really love to hear what you master tuners and long time PCP shooters/tinkerers have to say about this. It doesn't even seem possible to have the same exact settings and have one velocity increase while the other decreases???

Thank you in advance for your help! Stoti
 
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Let's just talk about the Wildcat for a second to use as an example of tuning.

If you set the reg to 130 bar and then start to screw the hammer spring in to increase the tension and shoot over the chrono, you will notice the FPS goes up. But only until you reach a certain point. Then it starts to go DOWN. That means you PAST the point of tune for that reg/HS tension. So you should back out the spring a little until the fps goes back up. And that will be the best tune for that particular reg/HS combination. If that isn't fast enough, say you want 900, you can't go higher with the spring because it will go DOWN. So you back off the HS about a full turn and go up with the reg pressure maybe 5 bar. Then shoot over the chrono and ease in on the HS until it goes up and stops, then starts to go down again. . That will be the new top end of the new reg/hs settings. As Tominco puts it "you kind of sneak up on the tune you want". 



I believe that is what you did to get those numbers to fall. The HS tension and the reg pressure work in harmony. If you go up on the reg pressure, you may not see an increase in fps. But if you go up a little on the reg and up a little on the HST, the FPS will increase and the system will stay tuned in "harmony".



Hope that helps a little



Crusher


 
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The pellet itself also enters into the equation. For example, when I was tuning my .30 Bobcat, I got to the point like Crusher said where more hammer spring started to decrease the pellet speed. That was with the 44.75 grain. However, I was alternating between the 44.75 and 50.1 grain pellets. And with the 50.1 grain pellet the velocity kept going up for almost another full turn... food for thought.
 
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 Thanks you guys. I understand what you're both saying. Crusher I didn't touch the reg. pressure, just the HS. I'm still trying to digest the erratic numbers with the 33.95gr. while the 25.4gr. pellets were doing exactly what I wanted them to. If I wouldn't have shot a string with the 33.95gr. I'd be jumping for joy right now because the 25.4gr are shooting at 948fps with super accuracy. The problem is that I want the gun tuned for the 33.95gr. because they're what I'll probably be shooting about 85% of the time. I was really hoping to have a sweet spot where both pellets would shoot great and then just have dope for both of them so I could switch back and forth whenever I wanted. That's how it was shooting before I adjusted the HS because I was looking for a little more velocity with the 33.95gr. pellets. It's just got me baffled that the numbers for the 33.95gr. are so terrible right now and the 25.4gr so great. I already backed off the hammer spring to just a tad tighter than it was before I started, unfortunately, I ran out of light to get any chrono readings tonight. I'm going to mess with it for as long as it takes tomorrow, quarter to half a turn at a time if necessary until I get it dialed back in. Worst case scenario, I can just put all the settings back to where they were before I started. With those settings I was getting 940fps with the 25.4gr and 835 with the 33.95gr, both were shooting very tight groups. I started messing with the hammer spring to get the velocity up with the 33.95gr. and hopefully increase accuracy even more. Thank you for your help, I'll let you know how it turns out after I get it all adjusted tomorrow. One last question Crusher and Centercut...It's going to be a pain in the ass removing the stock and putting in back on after every adjustment. Is there any problem doing the velocity testing with the stock off? Can I shoot disassembled or do I need to put the safety? HS adjustment knob? or whole stock back on to test? If I can test while mostly disassembled it will cut the tuning time by 90% Thanks again you guys! Stoti
 
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Let's just talk about the Wildcat for a second to use as an example of tuning.

If you set the reg to 130 bar and then start to screw the hammer spring in to increase the tension and shoot over the chrono, you will notice the FPS goes up. But only until you reach a certain point. Then it starts to go DOWN. That means you PAST the point of tune for that reg/HS tension.

Crusher

Click to expand...

My experience with regged guns is when the hammer spring tension reaches a certain point, velocity stays exactly the same and it just uses ( wastes ) more air. 
 
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Stoti hi,

Right my Crown .25 was shooting Kings 25.39 890 fps average with e/s 13 s/d of 4.1

King heavy Mk2 avge 816 fps s/d 4.1 e/s 13. 

130 bar reg as set by Importer for 25 grain Kings. So so accuracy which I put down to me. Wanted to shoot heavies at 110 yards ( 100 metre range here) 

So on/off stock hst and Safety. 

After 1 turn heavy 824 fps average strip down hst 2.5 turns, still slider able to move freely about 12 mm

Chrono now with Heavy mk2 - 829 fps average, e/s 33 s/d 13.1. Max 849 fps ?? 

Another strip down.

Tightened the b....y m3-10 machine screw too much result allen head strips. B...r. Started to drill it out as those screw remove sets won't fit.

Having to buy more of those M3-10 machine screws. Clearly non intended to be on and off much.

Oh and reassembling , stock made contact with regulator plastic cap which popped out. Are they glued on or just push fit. Fragile anyway.

Cannot test more yet but looks similar to your findings.

Assume have to now fiddle with reg pressure.



safe shooting






 
Upvote 0
So check this out... I read the thread at the beginning and have been contemplating the adjustment of my hammer spring tension too, so I did it. There are some very strange results I'm hoping someone can make sense of.

MY Crown's regulator is set at 140bar, power wheel .25-.30, and the hammer spring adjustment set on high. The velocities before adjusting the hammer spring tension were verified by many, many shot strings and averaged as follows: 

JSB 25.4gr. - 940fps.

JSB 33.95gr - 835fps.

After tightening the hammer spring tension about half way, these are the velocities I got:

JSB 25.4gr. - 948fps (average of a 10 shot string) deviation was 11fps and the velocity average went up about 8fps.

Here's where it gets totally whacky...

JSB 33.95gr. - 800fps (average of 11 shot string) the maximum deviation was 47fps. The shot string looked like this: 793fps, 812fps, 812fps, 773fps, 820fps, 785fps, 815fps, 796fps, 790fps, 802fps, 778fps. 

After getting these numbers, I am absolutely stunned and baffled. I don't know how these numbers are even possible or what could cause this kind of shot sting. The velocities decreased over all of the previous shot string averages by 35fps and the velocities are totally up and down with the deviation average of 47fps. SAY WHAT???

I got some good advice from what of the most knowledgeable members of this board who told me to tighten the hammer spring tension all the way and lower the regulator pressure to around 120 and work my way back up. The gun is still super accurate with the 25.4gr. pellets and surprisingly accurate with the 33.95gr pellets too. The inaccuracy with the heavier pellets can totally be attributed to the velocity deviation.

I would really like to hear anybody's thoughts on my situation and hopefully get a dialogue started as to what could be causing one pellet to increase in velocity, have a small average deviation and remain accurate while the other pellet has a decrease in average velocity, and an average deviation of 47fps. 

Please help!!! I'd really love to hear what you master tuners and long time PCP shooters/tinkerers have to say about this. It doesn't even seem possible to have the same exact settings and have one velocity increase while the other decreases???

Thank you in advance for your help! Stoti
Click to expand...





Looks like you went too far, hence the erratic numbers.

The way to do it properly, is to set your reg. pressure as desired, 140 bar in your case. 

Back out the set screw of the hst sliding block (anti clockwise)

Set hst adjuster to "max"

Work your speed up by turning the set screw in (small increments, clockwise diirection.)

Make sure to use a chrony (kind of mandatory for this job) and look for the peak where the speed will not increase anymore. 

Turning in any further will actually lower the speed, and make the gun inconsistent. (This is the case with all FX airguns.) 

Done:)
 
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If you try to lower the hammer tension wheel from max, and down to 5-4, and so on, and hardly gets any more speed, you probably can just increase the regulator pressure some more. If you do not need to use the lower settings on hammer wheel for low velocity, you can just turn the wheel down a step or two, if the hammer strikes to hard. That allows you to finetune with reg pressure instead, without the need to take the stock off and adjust the screw every time.




 
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My comment here may not be very popular, but these FX air rifles are very well optimized at the factory. Seriously, they are very well tested in Sweden and again tested at the importer. They pretty much shoot MOA or better at 100 yds. as delivered. Velocity and pellet weight are simply parameters to the end goal of hitting your target. The Crown in 25 with the new X barrel was designed and tuned around the JSB 25.39 grain pellet. If you are not hitting your target, I suggest you practice more and tune yourself not your Crown. It could prevent a seriously expensive repair bill at the importer. These rifles are surprisingly delicate and if you don't know what your doing, serious damage can result. There is a great deal to optimizing a rifle for a heavier pellet many of those parameters are with the barrel twist and choke that you, as the turner have no control over..
 
Upvote 0
My comment here may not be very popular, but these FX air rifles are very well optimized at the factory. Seriously, they are very well tested in Sweden and again tested at the importer. They pretty much shoot MOA or better at 100 yds. as delivered. Velocity and pellet weight are simply parameters to the end goal of hitting your target. The Crown in 25 with the new X barrel was designed and tuned around the JSB 25.39 grain pellet. If you are not hitting your target, I suggest you practice more and tune yourself not your Crown. It could prevent a seriously expensive repair bill at the importer. These rifles are surprisingly delicate and if you don't know what your doing, serious damage can result. There is a great deal to optimizing a rifle for a heavier pellet many of those parameters are with the barrel twist and choke that you, as the turner have no control over..
Click to expand...


I'll have to disagree with you since my new 700mm Impact .30 came with the regulator set over 220 bar. Velocity was all over the place from 450 to 650 with a 50.15g JSB. 20 minutes tuning had it sorted out and performing well. Any level of quality control or testing would've spotted this problem. Looks like demand is so high that FX is bypassing most of their QC to fill orders faster.... or maybe one slipped by.
 
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Weatherby

At 130 bar can I expect Mk 2 heavy to reach say 840 to 860 fps? Having seen erratic fps with increased hst via slider I assume too low reg . Previous setting of slider was consistent 818 fps.



safe shooting
Click to expand...



Hey wolfie, I had mine shooting the 25 heavies at about 268m/s.

Reg. was set to 160bar, and adjusted hst slider set screw carefully until it didn't gain any speed anymore.

Barrel was a LW poly without choke, that might make a slight difference as well.



Cheers,



Gijs
 
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I believe there might be some missunderstanding regarding the term "maxed out hammer spring". As far as I know most use the term on most guns when they adjust hammer spring at a given reg pressure until there is no more velocity to gain. That is usually the max setting for that given pressure. But regarding the impact and crown, some refers to the maximum possible tension on the spring achiveable mechanically by adjusting the screw on the wheel all the way until it almost have no slack. If you max it out mechanically, you probably has to start measure pellet speeds at lower settings like starting on setting 1 or 2, and then measure one click up at a time. Lets say you end up with setting 4, and 5 have equal speed, you are probably maxed out already at setting 4, or somewhere between 3 and 4. So to find your "max" in regards to the reg pressure you have to measure the lower settings first, to know where you are in the adjustement range.
 
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