Tuning consistency

[Master of Disaster]

I'll say up front that I'm relatively new to PCP tuning. I'm having troubles getting a consistent tune. Here's what I'm trying to achieve:

Setup: FX Maverick 700mm .22 with 11 gram hammer, Huma pellet probe and hammer spring, shooting through the slug transfer port.
Pellet: JSB Exact .22 Monster redesigned
Goal: consistent speeds around 950 FPS

And here's what I did:
- Find the regulator pressure resulting in a plateau of 1000 FPS at maximal hammer spring tension. This turned out to be 120 bar on the rear regulator, so I set the front to 150 bar for a 30 bar difference.
- Turn back the hammer spring tension to find the 95% optimum at 950 FPS. This turned out to be half way the preset wheel (4 out of 7). The difference between 4 and 5 is quite big (940 at setting 4 and 970 at setting 5). I tried to finetune using the preload screw, but that didn't do much.

I now have an average of 940 FPS, but the spread is quite large (range from 920 to 975, not changing the hammer spring tension). At 100 meters, I can also see that the rifle is not very consistent.
What would the more experienced people around here advice me to do to achieve a more consistent FPS? Lighter hammer maybe? Or more pressure? Any advice is appreciated!

 

[dens228]

I would lower the second reg a bit and try to have the hammer spring at 6. My first guess, and there a people here that would know more than me, is that you are getting a consistent valve opening on the shot.

 

[Trucker3573]

What worked with my Maverick is finding the reg pressure that produced the velocity I was targeting with the wheel maxed at 7. I would set the reg, turn the internal adjuster way in, set the wheel at 7 and shoot over the chrono. I would then start working the internal adjuster up until speed maxed and held steady at PW 7. If that was the correct speed I would turn the adjuster just a tiny tweak back in and shoot the gun on 7 wheel. If it isn’t the correct speed then you adjust the reg and start over. Doing this gives my gun a less than 10 fps spread. It stays relatively consistent on wheel 6 but goes to hell pretty quick as you go down. This is ju at what I have found. Others may vary in experiences.

 

[bcsquared]

What worked with my Maverick is finding the reg pressure that produced the velocity I was targeting with the wheel maxed at 7. I would set the reg, turn the internal adjuster way in, set the wheel at 7 and shoot over the chrono. I would then start working the internal adjuster up until speed maxed and held steady at PW 7. If that was the correct speed I would turn the adjuster just a tiny tweak back in and shoot the gun on 7 wheel. If it isn’t the correct speed then you adjust the reg and start over. Doing this gives my gun a less than 10 fps spread. It stays relatively consistent on wheel 6 but goes to hell pretty quick as you go down. This is ju at what I have found. Others may vary in experiences.

I was about to suggest this method as well. This set up allows you to use the preset wheel to quickly change speed for specific pellets.

Have you watched AEAC's YouTube videos on tuning? I find them quite long but his methodology and explanation helps a lot.

 

[Trucker3573]

I was about to suggest this method as well. This set up allows you to use the preset wheel to quickly change speed for specific pellets.

Have you watched AEAC's YouTube videos on tuning? I find them quite long but his methodology and explanation helps a lot.

Using the wheel just depends on how picky you are about consistency. I think I am a bit overly picky as I don’t touch the wheel. I just leave it at max consistency and shoot jsb 25.39 and hades with it. If I were to go heavier I’d just retune.

 

[Master of Disaster]

I was about to suggest this method as well. This set up allows you to use the preset wheel to quickly change speed for specific pellets.

Have you watched AEAC's YouTube videos on tuning? I find them quite long but his methodology and explanation helps a lot.

Yes, I did watch AEACs videos and actually used them as my main source to tune the gun the way I described. I'll try to see if I can achieve better results with the method @Trucker3573 described.

 

[Trucker3573]

Yes, I did watch AEACs videos and actually used them as my main source to tune the gun the way I described. I'll try to see if I can achieve better results with the method @Trucker3573 described.

Also, mine did eventually start throwing errant low velocity shots. I ended up sending it to FX. It just arrived back but I haven’t had a chance to test it. They said the cocking rod was bent and something else with the hammer. So could ultimately be a gun thing too.

 

[weevil]

There’s nothing wrong with the method you used to set the HST. The wheel just provides presets and it’s the actual HST screw behind the wheel that matters. First thing to check is that the aforementioned screw is holding firm. There’s another screw inside the assembly that holds it firm - make sure that’s tight and it doesn’t hurt to put a little blue loctite on the actual HST screw. Second, if the gun is pretty new, the reg may be breaking in and not refreshing adequately between shots, causing speed variation. Check the gauge between shots to see how that’s going. You can always dry fire a couple hundred shots (with air of course) to break it in. They usually need a second (fine) tune after the reg settles in and I’d advise settling it at 97% of max (rather than 94) which will give a better ES.

 

[Solo1]

Use the p port too not slug I’ve found better consistency that way

 

[Airgunmann]

I'd also make the difference between the regs higher probably by lowering the rear reg I would shoot for 40 to 50 bar difference between the front and rear reg

 

[Dairyboy]

I’d advise settling it at 97% of max (rather than 94) which will give a better ES.

This. I'd say 3% is the sweet spot usually on a tune. I've gone to 4% but going further usually results in greater ES.

 

[Stubbers]

Weighing pellets helps a lot, .1 grain can be 1fps, so 1 grain could be 10 fps (this depends on a few variables).

Tuning to 980~ fps if your plateau is 1000 fps would be much more ideal for tight es. 2-3% is better than 5% for sure.

-Matt

 

[Bravo1956]

Turn 2nd reg to 100 bar, leave 1st at 150, turn wheel to 7, now shoot, see fps, keep moving micro adj screw counterclockwise until you reach 940.
I personally have found that with my 25 cal Sniper that low reg, high hammer is much more consistent. My 2nd regbis at 92 bar, total hammer adj length is 19.85 mm and I am shooting 34gr at 900 fps.
Also great advice in previous post, I removed hammer adj screw and installed a small cut piece of a semi hard plastic and my screw can adj but will never move or loosen from shooting.
I also have 11gm hammer.

 

[TheCarFather]

I've found on my 600mm 25 caliber Maverick that my fps spread gets worse as I move down on the power wheel settings.

When I tune I shoot the heaviest projectile I want to shoot and get it dialed in on PW7. So my tune is created shooting 34gr pellets on PW7 at 915fps, and I get my tightest fps spreads with that combo.

But I also like to shoot the lighter 26.6g Atomic pellets, which requires me to dial down to PW5 to keep them around 920fps. But I've noticed my spreads increase at PW5 or less. Both PW7 and PW6 are very consistent. I've just assumed it's a trade off for having the ability to adjust power output on the fly.

The rifle still shoots very well on the lower power wheel settings, just not as "perfect" as the 2 highest power settings.