Tuning Velocity/Accuracy Nodes

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Shootersbench

Shootersbench

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Jun 29, 2021
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Nampa, Idaho, United States
I am from the firearm industry and made the mistake of pulling the trigger on an air rife a few years ago and as they say.... "the rest is history. " I deal in most genres of the firearm industry i.e. benchrest, PRS, precision reloading. Often in firearms you will find accuracy nodes in your velocity, such as benchrest shooters often shoot between 2850fps and 2900fps (6mm-6.5mm); however one can find accuracy nodes at faster and slower velocities, in large part due to barrel harmonics. It should be noted that they deal with pressures exceeding 55K PSI, which exacerbates the harmonics. My question is, are there accuracy nodes in pellet velocities, and if so, what are some recommended velocities for some of the popular pellet's (.22)? For instance, if you can stabilize a Berger 105g Hyb Trgt between 2850-2900fps you should shoot 1k yds sub MOA, regardless of platform. 
 
most 22cal 14-18 gr are at 850-890 some faster with all the different barrels and twist rates . the sound can be herd very well from a fine tuned air gun, lotta hammer spring gun will feel and sound jumpy to me and you can here the wasted air very easy once you have tuned few guns its very noticable when your harmonics are way off by feel and sound and your chrony numbery will deffinitly show you when you gun is in tune or way out of tune. as far as nodes my ear and accuracy is my node and recorded pellets in flight will sure show you if your dirty air and or speeds are way off the charts just my opinion as im just a average guy that works with very little tools i sure can get the job done though also at shorter distances you can get away with silly speeds but once you reach out farther it will really affect accuracy
 
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880-900 is a really good spot for standard diabolo pellets at the 16-18:1 twist rates my air guns seem to have.

when you get heavier, longer projectiles, then they seem to like to go a little faster like 900-1000 (and spin faster) to stabilize properly, and end up doing better at longer range. slugs especially seem to like 1000-1050 in a lot of guns, but also do well at slower speeds for some people too.

i shoot jsb 18gr .22 at 860 (daystate revere) and 880 (taipan mutant) and jsb 25gr .22 at 940 in my huben k1.
 
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I have found some nodes at various velocities. As stated around 880-890 is a good start but I have also found 920, 935 and 950ish all have good accuracy and I consider them nodes for that purpose.

While there may be others that is what I have found using .22 caliber, 18.13gr pellets. My friend also shoots the 25.39, .22 caliber pellets and is at around 950ish as well.

Of course, you know that each barrel will have different nodes, so some experimenting on your part is necessary, but this is my experience.

mike
 
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This last weekend I was tuning my .22 FX Maverick for JSB Monster RD's(25.39gr), JSB Beasts(34gr) and some 26gr-30gr slugs. The RD's I aimed for 970-980fps which I know they are good for, the Beasts at 905 - 910 and slugs around 990fps. Once finished I decided to try the JSB Heavies(18.13gr), albeit at lower power wheel setting which turned out to be 1010-1020fps!! Many would say way too fast for 18gr diabolo pellets, my self included, but I have stumbled across some magic for these light pellets. I shot a dime size group with 5 shots at 40m(44yds) in strong wind, I could not believe it, so tried again, same result dime sized 5 shot group, and repeated it again...... 3 dime sized groups at 1000+ fps!!

Conclusion, do not be afraid to experiment, you could be surprised!!

FX Maverick Sniper(700mm) .22 cal with Superior Heavy liner, 1:16 twist rate.
 
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There are a few different things in play here.

First is stability of PELLETS. Pellets are largely drag stabilized, so the concern is usually around shooting them too fast or in a barrel with too fast of a twist rate and have them start spiraling. Pellets are usually happy at or below their optimum stability ceiling, which for 'normal' pellets is ~900fps (super heavy pellets like Monsters it is higher). Pellets are very forgiving if not over-driven. Some people do find accurate speeds above this like in the comments above, but that shouldn't be counted on. The most common 100yd competition pellet tune is .30 JSB 44.75gr pellet in the 850-910fps range

Second - stability of SLUGS. They behave more like bullets and you need to have the right twist rate, and the barrel has to 'like' the slugs. Unlike pellets, they can be accurate up to the sound barrier, and you might see a preferred speed they don't like to be shot UNDER. A lot more trial and error in the realm of slugs. 

Third is the barrel harmonics you talk about. Yes that is in play for PCPs, but it can be different for each gun and tune. Probably shows up more significantly if you have a more violent shot cycle with the gun maxed out shooting slugs at 1000+ fps, vs shooting pellets at 880fps. I suspect this is another reason why pellets are more forgiving - pellet tunes are usually very mellow. My slug experimentation topped out at 97fpe, which is 78% of the 124fpe FX claims the M3 Impact is capable of. My .30 Impact didn't exhibit much speed preference with regard to slugs, it seemed to either like the slug or not, and shot about the same at different speeds. Group sizes varied by maybe 1/4-1/2MOA between best and worst speed. Hard to say how much speed preference is due to harmonics vs other projectile factors, but in the end if it works, it works!

Pay attention to what has been said about tuning not to waste air. For best results, tune for ~95-97% of the max speed at a given reg pressure. If you are at 100% then the valve is going to be open when the projectile leaves the barrel resulting in turbulence, noise, and wasted air.
 
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There are a few different things in play here.

First is stability of PELLETS. Pellets are largely drag stabilized, so the concern is usually around shooting them too fast or in a barrel with too fast of a twist rate and have them start spiraling. Pellets are usually happy at or below their optimum stability ceiling, which for 'normal' pellets is ~900fps (super heavy pellets like Monsters it is higher). Pellets are very forgiving if not over-driven. Some people do find accurate speeds above this like in the comments above, but that shouldn't be counted on. The most common 100yd competition pellet tune is .30 JSB 44.75gr pellet in the 850-910fps range
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Most people consider it is drag stabilized but it's actually called flare stabilized, pellets don't really have a large drag surface to stabilize it.

Pay attention to what has been said about tuning not to waste air. For best results, tune for ~95-97% of the max speed at a given reg pressure. If you are at 100% then the valve is going to be open when the projectile leaves the barrel resulting in turbulence, noise, and wasted air.
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If you want to waste air you tune for around the max speed at a given reg pressure ;) I know they mention this in a lot of youtube videos but it is far from the most efficient tune. It is an easy start to learn to find a stabile harmony point of hammerspring tension with reg pressure but it is for sure not efficient. Have a look at this: link to instagram post. This is measured with a constant muzzle velocity over the whole pressure range. If you scroll down in the feed you'll find more examples of researches for maximizing shot count (which is still not the most efficient in terms of air consumption per shot). The magic of the FX Impact is in the valve return spring, this will allow you to reach super low velocity spread anywhere on the hammer spring scale. High pressure is key for minimizing wasted air. Want to achieve maximum efficiency with FX rifles: find the reg pressure at which the desired velocity is reached and increase the pressure by about 20% and tune to your desired velocity, you'll get 15 to 20% extra shots from a the same fill compared to the Youtube tune 😁
 
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If you want to waste air you tune for around the max speed at a given reg pressure ;) I know they mention this in a lot of youtube videos but it is far from the most efficient tune. It is an easy start to learn to find a stabile harmony point of hammerspring tension with reg pressure but it is for sure not efficient. Have a look at this: link to instagram post. This is measured with a constant muzzle velocity over the whole pressure range. If you scroll down in the feed you'll find more examples of researches for maximizing shot count (which is still not the most efficient in terms of air consumption per shot). The magic of the FX Impact is in the valve return spring, this will allow you to reach super low velocity spread anywhere on the hammer spring scale. High pressure is key for minimizing wasted air. Want to achieve maximum efficiency with FX rifles: find the reg pressure at which the desired velocity is reached and increase the pressure by about 20% and tune to your desired velocity, you'll get 15 to 20% extra shots from a the same fill compared to the Youtube tune 😁
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I don't have an instagram account so I am unable to see the post you refer to (I know I'm not the only one who refuses to deal with the social media companies). Can you repost or at least summarize the content here?

The 95-97% tune credit goes to Bob Sterne I believe, at least that is the first place I read about it: https://hardairmagazine.com/ham-columns/tuning-regulated-pcp-airguns/.  Yes, it is a generalized technique, but I like it because it is easy to do and is going to give good results on just about any PCP without extensive experimentation. I would love to hear more about how to optimize for shot count while maintaining the same velocity spread, even if it only applies to FX rifles and/or the Impact. I don't think I've seen that discussed to date and I suspect that Instagram post has the testing that a lot of us wish we had the time/resources to do but can't.
 
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Want to achieve maximum efficiency with FX rifles: find the reg pressure at which the desired velocity is reached and increase the pressure by about 20% and tune to your desired velocity, you'll get 15 to 20% extra shots from a the same fill compared to the Youtube tune 😁

My question:

What hammer spring tension do you use to find this reg pressure that gives your desired velocity? I understand fine tuning will happen afterwards, but I am interested in what you use as you go through the different reg pressures?

Regards.


 
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@



Want to achieve maximum efficiency with FX rifles: find the reg pressure at which the desired velocity is reached and increase the pressure by about 20% and tune to your desired velocity, you'll get 15 to 20% extra shots from a the same fill compared to the Youtube tune 😁

My question:

What hammer spring tension do you use to find this reg pressure that gives your desired velocity? I understand fine tuning will happen afterwards, but I am interested in what you use as you go through the different reg pressures?

Regards.
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sorry for the delayed response. I just look for the hammer spring tension where the velocity starts dropping (just in front of the velocity plateau). I quickly look for it with the numbered dial and finetune it with an allen key with the MKII or the speed dial system in the M3.
 
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