Tuning This does not make sense...

[Raindance]

Hi O wise ones, I have come to seek your advice.

While tuning my Maverick I am getting results that I do not understand and seem to go against all I have learned about tuning PCP's. The following results are optained from the following:

FX Maverick Sniper,
Superior heavy 700mm slug liner,
Power probe and 11g hammer weight,
Javelin 30G slugs,
Reg1 @ 160 and Reg2 @ 120,
Bottle at 250 to 220 bar,
IHS adjuster tuned max (Results obtained pre fine tune)

At these settings the chrony shows on HS setting 1 the gun is shooting at average 940 FPS, turning it up to the highest setting (7) the velocity drops to around 865 FPS.
This is exactly the opposite of what I am led to believe should happen and is seriously screwing with my tuning attempt. What is going on???

Any advice, comment and insights will be highly appreciated.

Thank you,

Regards

 

[ram2jeep]

That does make sense. It just means that your adjustment is off. You would either need to increase regulator pressure or turn your adjustment screw clockwise until the fps goes the other direction.
It has happened to me and the above recommendations fixed the issue. It does seem counterintuitive but that is the way. On the tuning videos they use a mm distance as a start on the adjustment screw but I found it didn’t work for me; each rifle is unique.
Hopefully some other’s will chime in but that was the solution for me.

 

[elh0102]

I can't give you a technically knowledgeable answer, but I know that the situation you describe is normal, and I think it relates to the length of time the valve is open, and I think yours is remaining open too long relative to the available air. This is why most folks aim for a tune that produces around 95% of the maximum velocity at any given reg set point. A smaller increase in HST might result in higher velocity, but it depends on where you are in the tune balance. My guess, you will have to increase your reg set point to take advantage of a higher hammer pre-load setting. Since air pressure is the horsepower in this engine, there is a maximum for any reg set point. I guess it's kind of like tuning a car engine in the old carburetor days. You could put on a huge carburetor, but if the piston compression, ignition, and valve timing weren't set up to accommodate it, you just ended up with a bunch of wasted fuel that didn't get burned. I'm sure a knowledgeable tuner will give a better answer.

 

[starlingassn]

sounds normal to me.

too much hammer strike for current reg pressure.

up the reg setting or back off the hammer.

you said you started with the wheel on 1 but maxed out the internal hammer adjustment to begin with,
you were probably already very near the top speed at that reg setting or possibly over it.

regardless of what number is on the wheel,
its still only controlling the strength of the hammer strike in conjunction with the internal adjustment.

(you could set the wheel on 1 and max the hammer spring,or you could set the wheel on 7 and max the hammer spring,
both settings would yield basically the same results since the end result is maxing out the hammer)

start at number 1 again but back off the internal adjustment some so you have some room to go up,
shoot it at each setting,
when you find the setting where the velocity stops going up or drops,
back the internal hammer off a little.


very similar to tuning my impact,

i get my reg setting i want,
start with the wheel on a lower number,
but i leave the hammer spring adjustment in the middle of its range,
start shooting and increase the power wheel till the velocity stops climbing,
then i back the hammer off till it drops about 15-20fps,
then i screw in the valve adjuster till it drops about 10 more fps (not applicable on your maverick)
done

 

[Raindance]

@ram2jeep @elh0102 @starlingassn - Thank you gentlemen, the penny is starting to drop, thank you. Been doing what you say and seems 137 on the second reg on setting 7 is doing the job. Still have to check the if the other (lower) settings now actually reduce velocity.
Clocking 1044 on 7 with 25.39gr Redesigns with a sdev of 2.6 at the mo.

Thank you once again gents.

Regards