Tuning Air Arms Diabolo Field .22 cal 16 grain - what would be the optimal speed?

Everything I have read says 800-950 fps. I imagine it depends on your elevation to avoid trans-sonic speeds within that window.

https://hardairmagazine.com/ham-columns/accurate-airgun-pellets-general-conclusions-and-data/#:~:text=22%20calibers%20substantiate%20the%20belief,the%20800%20%E2%80%93%20950%20FPS%20range

I shoot these out of my Kral NP03. That rifle has a short barrel and is very accurate in the 820ish range. My FX dreamline shoots them well around 880. Let the fun begin!!!

Optimal and best are at best moot terms when used here. I have shot the .22 JSB, Air Arm, FX Diabolo pellets at anything from 630-860fps in several guns and got excellent accuracy at many accuracy nodes. So it depends on the individual gun, tune, use and how fast you want to shoot them. It is widely accepted that the Diabolo pellet is most accurate in the 800-830 fps range though. Still they shoot excellent from many guns at far lower or a little higher velocities as well.

So generally they shoot best at the speeds mentioned above. I believe to get best accuracy from them you need to try different speeds and see what works best.the reason for this is barrel harmonics. At least that's the main reason. If you go over the speed of sound weird stuff starts happening anything lower than that the speed of sound is most likely caused by the pellet leaving the barrel on a high or low point of vibration. Imagine a tuning fork and how it moves from one side to the other while it vibrates. When you find the sweet spot what your doing is finding the fps where the pellet leaves the barrel when the vibration from one side to the other is right in the middle. You can't eliminate barrel vibration. You can reduce it and find the spot where it has minimal effect. you should look up a video on barrel harmonics. Matt Dubber has an excellent video on his YouTube channel. However if you just want a quick answer try tuning it to the lowest velocity you can deal with and slowly go up shooting groups and see when accuracy is diminished then go back to where it was most accurate. Generally 800 to 950fps or somewhere around there.good luck buddy hope that helped. Reading it back to myself I'm not sure I did a great job explaining. Definitely watch that video he does a much better job. 

You just have to shoot it and determine the best speed for your rifle. If you use 880 fps as a starting point, you probably won't be far off. Once you find the velocity you like, then you can check your hammer spring tension relative to the maximum velocity at the current regulator set point. If you are substantially out of balance, then you might want to adjust the regulator. 

Anywhere from 500-960fps works great for me 

My PP700 likes them in the 650 area. It one holes it in my backyard 18y target

Anywhere from 500-960fps works great for me

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You know...this was really helpfull, thanks for your time posting it

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Sure, I'll make sure not to respond to your posts in the future 

The reg is at "factory settings" how Edgun just put it together.

And sound like a "real thing" .

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Attila,

I understand from your comment that the gun sounds loud, like a "firearm" shot?

Then you mentioning the regulator and the MV is the right path. Likely the hammer gets hit too hard for the current regulator setting, so that a lot of air is uselessly blown out the muzzle long after the pellet left.

To get a PCP quieter, shorter sips of higher air pressure will be your ticket == shorter sips (lighter hits of the hammer on the valve) of higher air pressure (higher regulator set point).

Nice gun!

Matthias

Nice gun!

Matthias





To get a PCP quieter, shorter sips of higher air pressure will be your ticket == shorter sips (lighter hits of the hammer on the valve) of higher air pressure (higher regulator set point).

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Okay, I've got a question. I have generally obtained most consistency by using a HST adjustment that is usually in the 95-97% range of the maximum velocity obtainable with the given reg setting. It seems, by going to a lighter hammer strike and higher reg setting, I would be getting further away from what has usually been my best combination. Maybe I just don't understand, which would not be unusual!

Ed

Ed, you understand just fine, likely better than I do! (I learned it on the forums, but there's much left to learn for me....) 



All I wanted to point out is that sometimes a gun is tuned inefficiently — and therefore could be much louder than necessary for a given power setting (with only a tiny gain).



And to point out that there is a way to make a gun much quieter in general (not just by the obvious route of lowering the power, but by changing how a certain power is achieved, "the tune" of shorter sips of air at higher regulator pressures).



Your tune of 95-97% of the max. power achievable at a certain reg pressure is getting the best of both (or all four) worlds: excellent power, not very loud (for the power achieved), excellent efficiency (power per air used), and excellent constistency of power (only small muzzle velocity variations).



Unless you need a really quiet gun and can't/ don't want to hang an Emperor silencer on it, you're probably best served by that tune.



To make my gun quieter, I increased the reg set point and reduced the hammer spring, giving me shorter sips of air at a higher pressure — at the same power/ muzzle velocity, going lower than the 95% mentioned.

The downside of going lower than the 95% of the max. power for a given reg setting — e.g., going to 90%, 85%, or 80% of max. power — is that small inconsistencies of the hammer striking and the valve opening and closing will have a bigger effect on the air flow, because the opening and closing is so minimal to begin with (short sips of air). And those mechanical inconsistencies in air flow produce inconsistencies in the power/ MV.

—> For shorter ranges with larger kill zones this isn't much of a problem. For target shooting it is....



Matthias

Okay, I've got a question. I have generally obtained most consistency by using a HST adjustment that is usually in the 95-97% range of the maximum velocity obtainable with the given reg setting. It seems, by going to a lighter hammer strike and higher reg setting, I would be getting further away from what has usually been my best combination. Maybe I just don't understand, which would not be unusual!

Ed

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you are 100% correct that best consistency is at the knee of the shot curve. However when it comes to less noise and efficiency lower hammer spring is better at the expense of super consistency. How much consistency is lost depends on the gun and transfer port size but the goal is to have the valve close well before the pellet leave the barrel. also with high reg low hammer tunes the gun is more sensitive to reg creep but nothing sry firing couple of times won’t fix. Best consistency is ES of sub 10 and SD around 2-3, hard to achieve. with high reg low hammer tunes the ES usually is between 10-20 and SD of around 6-8. 


generally I use high reg and low hammer tune for back yard shooting so it’s as quiet as possible, accuracy is more than good enough at 30 yards. 

Thanks for the clarification, it makes sense. I have a couple of rifles with easily adjustable hammer springs, and I'll sometimes turn them down quite a bit for yard plinking. And I observed just what you described, less noise with less consistency, but not a factor when shooting at such close range.

Sounds like you have a handle of what to do now. Personally I shoot those pellets from 840-920fps normally. I also shoot them in one gun at 620fps and it does very well there too.