I am curious about how efficient setting of the pellet velocity via a hammer spring adjuster versus the harmonic tune (adjusting regulator pressure, hammer spring and some times the port size). I have read many posts and watched videos talking about getting the most out of a PCP by tuning both reg and hammer spring (and port size, if adjustable). I have also read about tuning for various pellets by just adjusting the hammer spring. What do you lose in overall efficiency and accuracy if you only use the hammer spring adjuster?
Hammer Spring Tune vs Harmonic Tune?
- Thread starter fderry
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I use a tensioning barrel system to overcome the harmonics. Its especially helpful in unregulated guns.
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I am not an expert, but if the gun shoots 850 fps with 97% of the peak velocity for a given reg pressure, and we tune the gun with higher regpressure, so the same velocity you had in previous tune is achieved at 90% of the peak velocity of the reg, I am guessing that the gun will be more efficient. But if you in the first example only has 180 bar left in your fill bottle, you may get more shots, as you can shoot further down on pressure (some shoot below regpressure). If you in the other hand has a compressor and can fill your gun to 250 bar, every time you take your gun out to shoot, you probably get more shots on the high reg tune. So it probably depends on your starting pressure, and the pressure you refill the gun at.
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If you rely solely on hammer strike to obtain the desired fps in a regulated setup, then you risk being tuned far enough away from the plateau ( peak potential velocity with the given combo of barrel length/pressure/port size/pellet weight) that you will see a higher extreme spread than if you were tuned within 3-5% of your plateau. Reason being, is variation in hammer strikes (a hammer strike is rarely 100% consistent with its transfer of kinetic energy and momentum, temp / humidity swings, shot angle, and RNG all come into play here), as well as variation in pressure holding the valve closed (a regulator is rarely 100% consistent when it comes to packing just enough air molecules prior to closing itself off from the high pressure air contained within a reservoir .)
Really the 'best' tune takes into account all variables, the pressure (relative to the desired power output so one can be within 3-5% of their plateau), port size (relative to the power one desires), and hammer strike (relative to the needed lift/dwell to obtain desired power)
Harmonics is a pretty subjective subject...you smack a valve with a sprung weight to release a certain amount of air, there is no way to 'harmonically' tune that aspect...getting 900 fps at 1800 psi is relatively equal to getting 900 fps at 2500 psi provided you port each one so their plateaus are equal...since both setups would have the pellet arriving at the muzzle at 900 fps, what exactly is harmonic tuning in an airgun? BEATS ME, but people swear by it.
The only way to 'vary' harmonic tuning is respective to the pellet position in the barrel relative to barrel movement, which means varying its speed. So in the end, what ultimately is the observable difference if you were to 'harmonically tune' an airgun? The harmonics, or the slight variation / change in fps? With AIR rifles, operating at sub 5k pressure, there really isn't much, if any barrel movement. Barrel harmonics are well known in the PB world, but IMHO, 'harmonics' are irrelevant for us air gunners, just as much as spin stability is to a diablo pellet. Just my 2c and nothing more.
-Matt
Really the 'best' tune takes into account all variables, the pressure (relative to the desired power output so one can be within 3-5% of their plateau), port size (relative to the power one desires), and hammer strike (relative to the needed lift/dwell to obtain desired power)
Harmonics is a pretty subjective subject...you smack a valve with a sprung weight to release a certain amount of air, there is no way to 'harmonically' tune that aspect...getting 900 fps at 1800 psi is relatively equal to getting 900 fps at 2500 psi provided you port each one so their plateaus are equal...since both setups would have the pellet arriving at the muzzle at 900 fps, what exactly is harmonic tuning in an airgun? BEATS ME, but people swear by it.
The only way to 'vary' harmonic tuning is respective to the pellet position in the barrel relative to barrel movement, which means varying its speed. So in the end, what ultimately is the observable difference if you were to 'harmonically tune' an airgun? The harmonics, or the slight variation / change in fps? With AIR rifles, operating at sub 5k pressure, there really isn't much, if any barrel movement. Barrel harmonics are well known in the PB world, but IMHO, 'harmonics' are irrelevant for us air gunners, just as much as spin stability is to a diablo pellet. Just my 2c and nothing more.
-Matt
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Some guns has not the option to change reg pressure without taking the gun apart. So the simplest way to tune thouse guns is to try different pellets with different weight, and adjust power with hammer spring force only. And then stop at the speed which give best groups on paper. A particular pellet might group best 100 fps lower than max, while another might group best 30 fps lower. Some never adjust theire reg at all. Also some guns can be adjusted over a relative wide speed range, with set regpessure, and still have relative litle variation in speed.
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Here is an example. I was recently tuning my Fx Dreamline. Reg at 150b, hammer spring 2 clicks under max. Groups with the transfer port set on .22cal were outstanding at 50yrds with the pellet going 865fps. All I touched was the power wheel and set it to .25cal which is a larger transfer port. The speed jumped to 890fps which isn't too fast for a pellet but my accuracy went to crap. Bottom line is by enlarging that transfer port and not retuning everything around it, my gun isn't right. If I absolutely would need 890fps and want the best accuracy, there really are no shortcuts. If you want the most out of your gun, you have to adjust your velocity with your reg, then dial it back a little with the hammer spring. If you don't ever want to touch your reg setting, you are going to have to be content with the velocity the gun gives you. There is some wiggle room if you want to increase or decrease velocity at a given set point but not much.
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Thanks for the replies. I have gone back and read some of Bob Sterne's articles on this subject and between your replies and his articles I'm getting a better understanding of the subject. Somebody should write a book call "Zen and the art of PCP tuning"!
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Transfer port adjusters as it relates to this post. My Bantam Sniper has six TP levels. I understand that the opening is constricted or opened. And that you don’t save air when you shrink the ports’ opening. I can go from 892 FPS with JSB 18s to 653 FPS with Crosman Premiers. My regulator is set at 150 bar, what happens to the air charge as the port is constricted. Where does the air not used as you shrink the port go? I hope I’m being clear, thanks.
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All air goes out the barrel no matter how it’s delivered. That’s why you can open everything up and have a fast gun that’s an air hog. It might not even be as accurate as it could be because of the turbulence from the huge blast. You can shoot 850 FPS at 150b with the port wide open and a light hammer strike or TP level 4 with a little more hammer strike. That’s when you compare the ES, amount of shots and accuracy of each setting and choose. If 892 is your wide open max, you don’t really want to be there.
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