Tuning General Operational and Math Question

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GerryR

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May 22, 2025
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I was just looking at different gun specs and came across a gun that has an 18" barrel, fill pressure of 3625 psi (regulator pressure not specified), and claims 985 fps and 35 fpe at the muzzle. I calculated that the pellet has to be 16 grains for this to happen.
Now, my gun has a 23.6" barrel, fill pressure of 3600 psi (regulated to 1800psi) and can get 900 fps with a 14.5 grain pellet, giving 26 fpe. The velocity would have to be increased to 1039 fps to get to 35 fpe. How would you go about tuning to get 35 fpe? I would think that with the longer barrel a larger blast of air would do it, so increase the hammer spring pressure or ??
 
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I think we all focus too much on fpe. I've shot small game, mainly squirrels, with airguns from 14 fpe to almost 50 fpe. I think once you get to the upper teens the gun will work as long as you hit the chest or brain. By the time you get up around 30 fpe, possibly 25 fpe, the chances of an animal running after a decent hit become small with no discernable difference with upper 40s fpe. I also do not find 25 calibers kill squirrels noticably quicker than 22s at equivalent energy.

So I do not really think you need to increase your fpe.

But if you want more, I think you need to start by testing different pellets to hopefully find one at least as accurate as the one you are using. Going to 1000 fps with a pellet is not likely to be accurate. You want to stay in the 800-low 900 fps range. So you can do the math to see what pellets would give you the fpe you seek. Then buy some and test them. You do not need to increase the regulator for this. Accuracy is not a strong function of velocity in my experience. I would test pellets first at your current tune and then try different velocities.

I don't like to use hammer speed to be more than a fine tuning way to set velocity. If I turn the velocity too low, more than 3-5% below the peak for that regulator setting, I have issues with first shot velocity and accuracy. I choose the final hammer spring setting by accuracy. The main way to increase velocity is to raise the regulator. That takes a little more effort and time with an internal regulator but on my guns it is still very possible and with practice I can change them in about 15 minutes.
 
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Each gun is different. Valving, regulator, plenum size, hammer spring and I've probably missed some, but you get the idea. For instance, my Crown 22 with 600mm barrel can comfortably hit 30+ fpe without any problem at something like 110 bar reg pressure. It can also go far below that and shoot just fine, just depends on the tune. Now, consider my Wildcat 22 with the same barrel, it has trouble going below 30+ fpe, and goes wild when tuned down. Same barrel on both gives wildly different velocities. The Crown, IIRC has a something like 54cc plenum, while the WC has an 89cc plenum. Same barrel, same regulator, only difference is the plenum, as I'm pretty sure they use the same valving, and hammer spring, but I haven't confirmed it.

Also, heavier projectiles will give higher fpe, so it's not likely you'll get your best power with light pellets. I think the Crown is rated at 54fpe max, and I seriously doubt you would get great accuracy and consistency with say, 14gr pellets, which would be something like 1300fps. I doubt that pellet would fly very well at that speed. A 25gr pellet would be a lot closer to ideal at 54fpe/985 fps, but still pretty fast. Go to a 26 gr slug, and you'd be looking at the sweet spot.
 
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DesertSilver said:
You forgot hammer weight and barrel length.
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How does the barrel length affect the velocity. That is what has me confused. The example I sited has an 18" barrel doing ~85 fps more than my 23.6" barrel with about the same weight pellet. I did play with the hammer weight a little by adding a small slug under the hammer spring, which also compressed the spring about one turn of its free length when installed. At first, the slug was twice the length of what is now in there, but it was just wasting air. The one I have in there now gave almost the same velocity as the thicker slug, but I get more shots per charge down to the regulator pressure. The added "pulse" of air from the heavier weight and loaded hammer spring still didn't get me the increase in speed that I expected, just wasted air. So there must be some optimum hammer weight/spring force for a particular setup(?). The heavier slug added 45 grns to the hammer and the thinner one 28 grns. The hammer weighs 739 grns.
 
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DesertSilver said:
The longer the barrel the more time the projectile has to accelerate. It just needs to be tuned to give enough air to push it the length of the barrel.
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That's what has me puzzled. With the larger slug that I used in the hammer, I merely wasted air; the smaller slug kept about the same velocity, but I gained in number of shots. Does that mean that the plenum is too small and cannot provide enough air for the barrel length, basically emptying out with the larger slug in there, but still not enough air to accelerate the pellet further down the barrel?
 
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GerryR said:
How does the barrel length affect the velocity. That is what has me confused. The example I sited has an 18" barrel doing ~85 fps more than my 23.6" barrel with about the same weight pellet. I did play with the hammer weight a little by adding a small slug under the hammer spring, which also compressed the spring about one turn of its free length when installed. At first, the slug was twice the length of what is now in there, but it was just wasting air. The one I have in there now gave almost the same velocity as the thicker slug, but I get more shots per charge down to the regulator pressure. The added "pulse" of air from the heavier weight and loaded hammer spring still didn't get me the increase in speed that I expected, just wasted air. So there must be some optimum hammer weight/spring force for a particular setup(?). The heavier slug added 45 grns to the hammer and the thinner one 28 grns. The hammer weighs 739 grns.
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Is the 18” barrel gun you refer too the same make and model gun as your 24” barreled gun? I didn’t necessarily get that impression from your first post.
 
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Just checking Gerry, since you did not mention the gun model - are you sure it is regulated? That could have a lot to do with it . . .

I have a .22 caliber Air Ranger with a 17" barrel, and it came from the factory set up as a 50 FPE gun, and it could do that with heavy pellets (it made 48 FPE with JSB Beasts at 33.9 grain, and I was able to tune it up to 50FPE). It is an unregulated gun, and the sweet spot of the power curve was 2900 psi at that power level (so a 3175 gave me about 25 shots with an ES of 1.5%).

I found I was able to easily tune it down by making shorter hammer spring spacers, and could set it up as low as about half the energy shooting 16 grain pellets at about 24 FPE - using about an 1800 psi fill for the same count and ES as above).

By the way, the gun stated that the max fill was 250 bar (so 3625 psi), but it would always be in at least partial valve lock at that pressure - it would fire, but at a much lower speed. I found no matter how I tuned it, the max fill for keeping it under 3% ES at max power was about 3300 psi. Also, the hammer in those 50 FPE Air Rangers is heavy - a bit over 100 grams if I recall correctly. That said, it has a great snappy shot cycle at the lower power tunes and is a joy to shoot like that, so that is where it lives now (~32 FPE) - I even fabbed an internal SSG for it so it works great as a very high shot count plinker too - if I'm willing to tolerate a ~70 FPS ES on a 930 FPS max speed, I get over 100 shots on a 2400 psi fill (shooting from 2400 down to about 1500 psi). That SSG made a huge difference on the backside of the curve, as the hammer used to bounce and waste air like crazy, but now it just fires once with a little less speed . . . .

Anyways, that is an unregulated data point at high power with a shorter barrel . . . .
 
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AlanMcD said:
Just checking Gerry, since you did not mention the gun model - are you sure it is regulated? That could have a lot to do with it . . .

I have a .22 caliber Air Ranger with a 17" barrel, and it came from the factory set up as a 50 FPE gun, and it could do that with heavy pellets (it made 48 FPE with JSB Beasts at 33.9 grain, and I was able to tune it up to 50FPE). It is an unregulated gun, and the sweet spot of the power curve was 2900 psi at that power level (so a 3175 gave me about 25 shots with an ES of 1.5%).

I found I was able to easily tune it down by making shorter hammer spring spacers, and could set it up as low as about half the energy shooting 16 grain pellets at about 24 FPE - using about an 1800 psi fill for the same count and ES as above).

By the way, the gun stated that the max fill was 250 bar (so 3625 psi), but it would always be in at least partial valve lock at that pressure - it would fire, but at a much lower speed. I found no matter how I tuned it, the max fill for keeping it under 3% ES at max power was about 3300 psi. Also, the hammer in those 50 FPE Air Rangers is heavy - a bit over 100 grams if I recall correctly. That said, it has a great snappy shot cycle at the lower power tunes and is a joy to shoot like that, so that is where it lives now (~32 FPE) - I even fabbed an internal SSG for it so it works great as a very high shot count plinker too - if I'm willing to tolerate a ~70 FPS ES on a 930 FPS max speed, I get over 100 shots on a 2400 psi fill (shooting from 2400 down to about 1500 psi). That SSG made a huge difference on the backside of the curve, as the hammer used to bounce and waste air like crazy, but now it just fires once with a little less speed . . . .

Anyways, that is an unregulated data point at high power with a shorter barrel . . . .
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I am new to airguns; what is an SSG? Also the gun in question is the inexpensive, Komplete. It is regulated at 1800 psi, though I have no way to verify it. I am very happy with it and am just trying to learn different ways of tuning it for higher power. Right now I'm getting about 32 fpe with HAWKi 25.3 grn pellets, which is fine for what I intended it for, but I couldn't reconcile the shorter barrel performing better than the longer barrel gun, everything thing else being equal, almost (I don't know the regulated pressure of the short-barreled gun.). But, what you appear to be telling me is that the pressure is much greater, 2900 psi, in the unregulated gun you have, and that is how your extra energy is accomplished (?).
 
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