HW100 picking up speed

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Capie

Capie

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Jun 16, 2015
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Cape Town , South Africa
Hi Folks. Need some guidance here please. My HW100 is acting up a bit. When filled to 180 bar it shoots perfect (785fps with 8.44gr 177 JSB's) but the moment the cylinder pressure starts to dip below 150bar the gun starts to pick up speed. At 110bar it is running at 840fps. It is a grudual climb in speed.

I replaced all the o-rings on the regulator, made sure everythng is nice and tight... yet the problem persists.

Any guidance would be greatly asppreciated.
 
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Did you set the reg with a tester, if so, what is the set point? I don't have the technical knowledge to offer an educated opinion, but I wonder if the reg set point and hammer spring tension are significantly out of balance and causing this behavior? I'm interested in the resolution, as I also have an HW100. Mine was a full power (FAC) version for the US market, but I have tuned it down to the level of yours. I did not experience any odd behavior in the tuning process.
 
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elh0102 said:
Did you set the reg with a tester, if so, what is the set point? I don't have the technical knowledge to offer an educated opinion, but I wonder if the reg set point and hammer spring tension are significantly out of balance and causing this behavior? I'm interested in the resolution, as I also have an HW100. Mine was a full power (FAC) version for the US market, but I have tuned it down to the level of yours. I did not experience any odd behavior in the tuning process.
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Hi elh0102

Reg is set at 85bar. When the cylinder is at 150 bar I get 625fps, at 120 bar it jumps to 770fps and at 100bar it goes up to 850fps...
 
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tcarlson777 said:
That sounds exactly how an unregulated gun would act. I suspect that your Reg is defective.
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Really? Let me show my ignorance here, because I thought velocity would generally vary directly with air pressure. In terms to accommodate the ignorant (me), can you explain what goes on with the valve and hammer relationship that produces higher velocities with decreasing pressure? I'm sure others would benefit as well, thanks.
 
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First off, I'm not an expert. When an unregulated gun has a higher pressure, it is harder for the hammer to open the valve, resulting in lower speeds, because the hammer can't fully open the valve. As the pressure falls, the same hammer strike can open the valve further, letting in more air, and then the velocity goes up. The general term for this relationship is the "curve". With fine tuning of the hammer spring, an unregulated gun can have a fairly consistent curve. A regulated gun should not experience this result, since the regulator keeps the pressure on the valve fairly constant. A good regulated gun should not have a "curve", it should have a pretty flat shot string.

Here is a helpful article on unregulated gun tuning: https://hardairmagazine.com/ham-columns/bobs-guide-to-tuning-unregulated-pcps/
 
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tcarlson777 said:
First off, I'm not an expert. When an unregulated gun has a higher pressure, it is harder for the hammer to open the valve, resulting in lower speeds, because the hammer can't fully open the valve. As the pressure falls, the same hammer strike can open the valve further, letting in more air, and then the velocity goes up. The general term for this relationship is the "curve". With fine tuning of the hammer spring, an unregulated gun can have a fairly consistent curve. A regulated gun should not experience this result, since the regulator keeps the pressure on the valve fairly constant. A good regulated gun should not have a "curve", it should have a pretty flat shot string.

Here is a helpful article on unregulated gun tuning: https://hardairmagazine.com/ham-columns/bobs-guide-to-tuning-unregulated-pcps/
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That makes sense. So, I guess the velocity would generally increase, then run relatively stable for a number of shots, until the pressure decreases to the point that the lower pressure becomes the limiting variable in the valve timing. ??
 
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sounds like the reg is actually set higher than the 85 bar,, probably about 120 to 150 bar
Velocity will climb when the hammer is not set high enough to match the plenum pressure. When the plenum pressure drops below reg setting, the valve is easier to open and lets more air out,, thus the increase in pellet velocity
either increase hammer spring or decrease reg setting to achieve a balanced condition ,, it is a balance of power ,,, plenum has power vs the hammer/spring has power,,, your plenum has more power in the OPs (original poster) setting
 
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Trampus99 said:
I had the same problem on my hw100 , I started out consistent and as air pressure dropped the velocity would raise. I found the hammer spring had been backed out ( probably in an attempt to increase shot count ) I turned it in clockwise 1/2 turn and my Spread went from 80 to 10.
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I think that demonstrates the importance of having a proper balance in your tuning. When I was tuning my HW100 down to the sub-12 fpe level, I played with the reg setting and hammer spring until I got the velocity I wanted at around 95-97% of maximum at that particular combination. My ES is among the lowest of all my rifles, usually single digit in a short 8-10 shot run. It's now great for yard shooting, still lethal on squirrels, and the shot count is great.
 
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Just an update on this: If all fails... start from scratch. So I detuned the gun and reset everything. Regulator reset down to lowest setting possible, then adjusted the hammer as it was too light. Tested and came out at 620fps. Redid the regulator and got the speed up to 745fps, with hammer maxed out. Reset the regulator and got to 812fps - target speed is 785fps for HFT. From 812fps I could simply adjust the hammer lighter until I reached the required speed.

Result: Happiness. The gun now shoots 8.44gr JSB's at 780 fps from a fill of 175bar all the way down to 90bar. STD of 6 (Pellets not weighed or sorted). As the regulator and hammer settle the STD will drop to the 3fps I am looking for.

Thanks for the input and assist. Much appreciated,
 
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Capie said:
Just an update on this: If all fails... start from scratch. So I detuned the gun and reset everything. Regulator reset down to lowest setting possible, then adjusted the hammer as it was too light. Tested and came out at 620fps. Redid the regulator and got the speed up to 745fps, with hammer maxed out. Reset the regulator and got to 812fps - target speed is 785fps for HFT. From 812fps I could simply adjust the hammer lighter until I reached the required speed.

Result: Happiness. The gun now shoots 8.44gr JSB's at 780 fps from a fill of 175bar all the way down to 90bar. STD of 6 (Pellets not weighed or sorted). As the regulator and hammer settle the STD will drop to the 3fps I am looking for.

Thanks for the input and assist. Much appreciated,
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That's great performance. Your tune is about exactly as mine. I'm shooting the 10.3 gr at 705 fps, at the same point on the power curve, and getting the same great consistency. We can go up to 20 fpe for HFT here, but mine is a backyard rifle and plinker. I might try the lighter pellet sometime as an experiment, think I still have some lighter ones in the old brown box Crosman Premier line.
 
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