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Education / Training Understanding the performance/power curve of a PCP

Understanding the performance/power curve of a PCP

by B.B. Pelletier

This final blog of 2008 was inspired by several questions from reader Kevin but also from other readers who are now owners of precharged pneumatic (PCP) airguns. I’ve written these things before, but perhaps never put them in the same order as I will today.

A PCP valve operates best between a certain high and low pressure point. That is to say the valve will open and remain open long enough to pass air from the reservoir to power a pellet to more or less the same velocity. When the reservoir pressure is high, it acts on the valve to close it faster, but the air that passes through the valve when the gun fires is under a lot of pressure. As you continue to shoot and the reservoir pressure drops, it acts with less force and less quickly on the valve to close it, so the valve remains open slightly longer. The air that passes through the valve before it closes is not pressurized as high; but since the valve remains open slightly longer, it delivers similar acceleration to the pellet. The result is that the pellet stays at the same velocity, more or less, throughout a number of shots.

The string of shots that are at the same velocity are the power curve of the gun. If the reservoir pressure is above the pressure at which this power curve begins, the shots will be slower. If the reservoir pressure is below the pressure at which the power curve ends, the shots will also be slower.

On either end of the power curve–before the curve begins (pressure too high) or after it ends (pressure too low), the pellets will exit the muzzle at a lower velocity than when the valve is dealing with pressure that’s inside the power curve.

As a gun that has been over-pressurized is fired, it loses some pressure with each shot. The pellets will come out progressively faster as the pressure drops, and you can actually record this if you have a chronograph. Then, at some point the velocity seems to stabilize at a level of similar velocities for several shots. That area is the right pressure for your valve and therefore for your gun. We call that area the power curve because it represents the place within the whole pressure curve (zero psi to the maximum fill pressure) at which the rifle operates the best–and also at the same power (more or less).

As you continue to shoot and the pressure in the air reservoir drops below the ideal operating pressure, the velocity of the pellets starts dropping below the ideal range. The decline can be either a straight decline with each new shot or the velocity can go up and down, but it’s always headed in a general downward direction. A powerful gun like the Career Infinity will usually drop velocity straight down with every shot when it falls off the power curve, while a less powerful gun like a
Benjamin Discovery may have velocities that go up and down; but the general direction will always be down from the ideal level (the power curve).

So, with yesterday’s 12-shot string that was continually declining with each new shot, I concluded that the rifle was coming down off the optimum power curve–a curve that would have been even higher than the 3,300 psi I put into the reservoir at the beginning. That’s why I said this in yesterday’s blog:

It seems as if the gun’s maximum fill is still higher than 3,300 psi, but I don’t have the pressure to go there. Nor do I think I would if I could. I’ve seen the walls of the reservoir, and they aren’t that thick. I recommend you do not overfill this rifle, because I don’t think there’s a large margin of safety. I did it to demonstrate that the valve was not yet on the power curve.

Do you understand? My last sentence, “I did it to demonstrate that the valve was not yet on the power curve” refers to pressurizing the reservoir to 3,300 psi after testing the rifle at 3,000 psi. Since each shot declined in velocity with a 3,000 psi fill, I boosted the pressure to demonstrate that the velocity would go even higher. I’d hoped the first couple of shots would be close to the same velocity with the 3,300 psi fill, but you can see that they’re not. Of course, that’s not to say that 3,300 psi isn’t the exact point at which the rifle drops off the power curve, and if I had pressurized the rifle to 3,400 psi I might have gotten those few close shots I was looking for. We’ll never know, because I don’t feel confident pressurizing this rifle any higher.

Kevin also asked why I said this–“the valve cannot function with pellets this heavy.” I was referring to some guns that will never have a power curve with pellets over a certain weight. You didn’t notice it because I didn’t report the shot strings. When I went to the lighter pellets, I got some shots of similar velocities. That was with the power wheel set on the lowest power setting. The rifle is very clearly on the power curve with lighter pellets and a lower power setting.

So, Kevin, the velocities I saw told me that this Infinity was not on the power curve with Eun Jin pellets, but that it was very much on the power curve with both Crosman Premiers and Air Arms Diabolo Field pellets. With the lighter pellets, I manipulated the power adjustment wheel to keep the gun on the power curve longer.

Kevin asked what I meant by a “broad flat spot on a power curve.” In this case, my answer looks better as a picture:

This is a typical velocity-over-pressure chart for a PCP. You get this by chronographing all the shots in a fill. If they look like this, you’ve captured the power curve, which begins at shot 15 (2600 psi) and ends at shot 27 (2150 psi). Filling this gun beyond 2650 psi is a waste of air, as is shooting after the 13th shot.
And, Kevin–every pressure above 2650 psi with this particular airgun is entering into valve lock.

Now you know it all!

author avatar
Tom Gaylord (B.B. Pelletier)
Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.

57 thoughts on “Understanding the performance/power curve of a PCP”

  1. Hi B.B.,I wish you and your family a happy,healthy and safe NEW YEAR.How do you safely clean light rust from the blued finish of valuable airguns and firearms without damaging it or scratching the blueing to much.I know that refinishing them is the kiss of death when it comes to value,but I just want to stop the spread of rust so it does’nt start pitting.Thanks for all the advice all year.JERSEY BOY

  2. I’ll say this about the A.F. Condor. You have three interrelated things that you have tweak and tweak some more to find the sweet spot(s) 1.The Top Hat 2.The Power Wheel 3. The optimum fill pressure. I personally had a hard time getting it out of my head NOT to fill to 3k. My gun seems to work best from 2500 down to 1800. Happy New Year everyone! From SavageSam

  3. B.B.,

    Fantastic! After I finished reading your post a bright light went of and is shining into the pcp world. I’m sure this is elementary to pcp users but for a springer guy like me entering the pcp niche todays post ties everything together in my little mind and now I understand the process of “finding the sweet spot” for each pcp. A chrony really is a must. This is the decoder ring.

    Thank you.


  4. B.B.,

    The graph is worth a thousand words.
    I’m assuming in your text, under the graph, you mean “Filling this gun beyond 2650 psi is a waste of air, as is shooting after the “27th” shot”? rather than 13th shot?


  5. B.B.,

    Well done! as usual…
    This one should be rerun often, with all the people getting into PCPs.

    The instinct is to overfill, thinking more pressure means faster pellet…

    The firing valve is the key to a great PCP. There needs to be a “consumer reports” on how each rifle preforms, on the PA website.

    There is such a thing on another website, and some high priced field target rifles have amazingly long, and amazingly consistent, (like 80 shots with 10fps spread) “sweet spots”, so it can be done..

    Perfecting that valve, and making it affordable in a quality air rifle, will make a lot of money for some manufacture…. Come on Crosman Disco!!! let’s hope…

    The Air Arms S410 does very well on their chart.. they rate it 5 on all counts, 5 being the highest rating..

    Ashland Air Rifle Range

  6. B.B. & Kevin,

    Also it needs to be more clear, that B.B. is using the power adjuster, and he is in the low setting at that time.. You said it above, but some people just scan and might miss it..


  7. B.B.

    looking back at mondays blog I had a thought about punches that I use and it seems pretty handy. I have a large variety of old rifle brass and when I need a hole (if I dont have a leather punch handy or the right size) I pick the empty case with the right size case mouth sharpen it with a deburring tool or chamfering tool, and whala I have a new punch good for a few holes.


  8. BB,

    This particular blog justifies why a chrono is essential…a must-have if we get serious with our hobby.

    I wonder, what about airguns which are set at the power curve but still groups really bad at the range? What to do in such cases?

    Thanks and Happy New Year to all.


  9. BB, what did you use to obtain the pressure left in the rifle after every shot? Do you have a guage hook-up that accurately measures the air pressure or are you relying on the rifle's built in guage? I'm curious because the Bemj Disco's guage does not give you a large enough scale to determine differences in pressure of 100 psi.

    On another topic, both my older air pistols, the Crosman 1300 and my S&W 78G stopped holding pressure. The Crosman has been successfully repaired with numerous trips to the local NAPA store to buy o rings. I only lost two parts but they affect the safety "only" (spring and ball bearing". I'll find them one day here in my little office. The nice thing is I learned a lot on how these little air guns work. The S&W is still minus one o ring and I might be forced to go on-line to a repair shop to order that one.

    Anyway, Happy and Healthy New Year to all, especially you, BB and Edith, and I look forward to seeing you again in Roanoke next year.

    Fred in NJ

  10. Lubricator,

    Thank you! You’ve given me a reason to save those .25 ACP cases I sweep up at the indoor range while recovering my .45 brass.

    Also, a golf club shaft is tapered and many have rings every few inches. Cutting them there makes another great set of graduated punches.


  11. Wayne,

    I only used the power adjuster on the last string of shots, which was number six. On the previous five strings the power was set to the lowest setting. So there really are five strings (30 shots) at 35+ foot-pounds in a (Infinity.

  12. B.B.

    For years I have picked up most the brass I see… bad habbit that comes in handy on occasion. The golf club idea is nice to, I have a few broken shafts someplace I think:)


  13. Fred,

    How you get the pressure after every shot is a backwards process. You shoot, then attempt to fill the reservoir and note when the inlet valve opens. It real easy with a hand pump, but terribly time, consuming. So most people just measure the first and last shots of the power curve that way and interpolate (guess) for all the others.

    Check with John Groenewold for those small parts:


  14. Abe,

    When accuracy on the power curve is the problem, another pellet is the solution. You haven’t found the right one yet.

    Or you could have a leaded barrel. When I was at AirForce and a rifle came in with accuracy complaints, the first thing I did was clean the barrel with JB Bore Paste. Then I shot a tight group at 23 yards and sent the very-accurate rifle back to the owner with instructions of how to clean the barrel and which pellets have to be lubed.

    In three year I found only one inaccurate barrel, and in the three years I have been gone, no others have surfaced.


  15. BB, off topic again – what do you know about the RWS/Diana 26? Is it a full-sized or youth rifle? I imagine it’s a lower-powered gun.

    A gun shop not too far from me has one for about $130. I haven’t seen it yet, but I’m sorely tempted to go check it out.

  16. I bought a 30$ 4×32 gamo scope for my benjamin discovery, I have never used a scope before and I looked up your guide here at pyramyd air to sight in the scope. Well, I followed that guide religiously and nothing was working. My scope seemed to not be adjusting. No matter how far I turned the clicking thingies. I thought I was obviously doing something wrong so I keep trying, but no matter how far I turned the clicking thingies, the shots were still going in or near the same place!!. So then I did a test, I shot one shot, and then I turned the clickie thingy that makes it go from left to right, and turned it all the way to the left. Fired a shot, and it was still in the same area. 🙁 This is really fustrating. Am I doing something wrong or is the scope broken? And yes, I took the caps off the knobs.

  17. B.B.

    Great, I look forward to that chart on the PA site..


    There are only a few pellets that will carry the energy out to 50 yards: On my Air Arms S410, when shooting at 20 ft lbs or more, crosman premium heavy 10.5 .177 does only a little better: 22 ft lbs at muzzle, and 13 ft lbs. at 50 yards, than the JSB 10.2 heavy; 22 ft lbs at muzzle & 12 at 50 yards, and the JSB 10.2 won't lead your barrel, like the CPH.. Logun Penetrators are also good..21 at muzzle and 12 at 50 yards..

    When shooting at 12 ft lbs muzzle, the the kodiak 10.6 are best on ft lbs at 50 yards (7 ft lbs), but JSB exact 8.4 and exact 10.2 heavy do a little better on accuracy for me.. and they almost are the same (7ft lbs) on ft lbs at 50 yards.. and the Beeman FTS 8.9 do well too.

    In .22 cal the 21 gr. Kodiak & Logun Penetrators, really shine.. in the .22 cal s410, they do 33 ft lbs at muzzle and 21 at 50 yards.. next are the JSB Exact at 30 & 17 ft lbs. at 50 yards…
    compared to the CP 14.3 at 28 muzzle, and 14 ft lbs at 50 yards.. or Superdome with 28 muzzle and 8 at 50 yards..

    Ashland Air Rifle Range

  18. Here is another example of “valve lock” in an older Classic Air Arms S410 .22 cal.

    AAs410 Classic .22 FAC
    9/12/08 2975 PSI Fill
    Grams FPS Ft/Lbs Brand
    1 15.9 845 25.2 At 205 BAR
    2 15.9 849 25.5 JSB Exact
    3 15.9 853 25.7 JSB Exact
    4 15.9 862 26.2 JSB Exact
    5 15.9 867 26.6 JSB Exact
    6 15.9 867 26.6 JSB Exact
    7 15.9 865 26.5 JSB Exact
    8 15.9 874 27.0 JSB Exact
    9 15.9 898 28.5 JSB Exact
    10 15.9 881 27.4 JSB Exact
    11 15.9 882 27.5 JSB Exact
    12 15.9 890 28.0 JSB Exact
    13 15.9 903 28.8 JSB Exact
    14 15.9 896 28.4 JSB Exact
    15 15.9 903 28.8 JSB Exact
    16 15.9 905 29.0 JSB Exact
    17 15.9 912 29.4 JSB Exact
    18 15.9 913 29.4 JSB Exact
    19 15.9 917 29.7 JSB Exact
    20 15.9 926 30.3 JSB Exact
    21 15.9 928 30.4 JSB Exact
    22 15.9 932 30.7 JSB Exact
    23 15.9 939 31.1 JSB Exact
    24 15.9 946 31.6 JSB Exact
    25 15.9 950 31.9 JSB Exact
    26 15.9 955 32.2 JSB Exact
    27 15.9 962 32.7 JSB Exact
    28 15.9 965 32.9 JSB Exact
    29 15.9 972 33.4 JSB Exact
    30 15.9 975 33.6 JSB Exact
    31 15.9 977 33.7 AT 180 BAR
    32 15.9 986 34.4 JSB Exact
    33 15.9 993 34.8 JSB Exact
    34 15.9 987 34.4 JSB Exact
    35 15.9 994 34.9 JSB Exact
    36 15.9 1000 35.3 JSB Exact
    37 15.9 1001 35.4 JSB Exact
    38 15.9 1002 35.5 JSB Exact
    39 15.9 1008 35.9 JSB Exact
    40 15.9 1006 35.7 JSB Exact
    41 15.9 1009 36.0 JSB Exact
    42 15.9 1005 35.7 JSB Exact
    43 15.9 1007 35.8 JSB Exact
    44 15.9 1004 35.6 JSB Exact
    45 15.9 999 35.3 JSB Exact
    46 15.9 999 35.3 JSB Exact
    47 15.9 999 35.3 AT 145 BAR
    48 15.9 994 34.9 JSB Exact
    49 15.9 988 34.5 JSB Exact
    50 15.9 986 34.3 JSB Exact
    51 15.9 983 34.1 JSB Exact
    52 15.9 980 33.9 JSB Exact
    53 15.9 974 33.5 JSB Exact
    54 15.9 967 33.0 JSB Exact
    55 15.9 959 32.5 JSB Exact
    56 15.9 959 32.5 JSB Exact
    57 15.9 953 32.1 JSB Exact
    58 15.9 947 31.7 JSB Exact
    59 15.9 939 31.1 JSB Exact
    60 15.9 928 30.4 JSB Exact
    61 15.9 929 30.5 JSB Exact
    62 15.9 924 30.2 At 110 BAR
    63 15.9 920 29.9 JSB Exact
    64 15.9 911 29.3 JSB Exact
    65 15.9 903 28.8 JSB Exact
    66 15.9 904 28.8 JSB Exact
    67 15.9 893 28.1 JSB Exact
    68 15.9 883 27.6 JSB Exact
    69 15.9 875 27.0 JSB Exact
    70 15.9 859 26.1 JSB Exact
    71 15.9 859 26.1 JSB Exact
    72 15.9 852 25.6 At 85 BAR
    73 15.9 840 24.9 JSB Exact
    74 15.9 822 23.9 JSB Exact
    75 15.9 802 22.7 JSB Exact
    76 15.9 808 23.0 JSB Exact
    77 15.9 797 22.4 JSB Exact
    78 15.9 782 21.6 JSB Exact
    79 15.9 787 21.9 JSB Exact
    80 15.9 781 21.5 JSB Exact
    81 15.9 768 20.8 At 70 BAR
    82 15.9 752 19.9 JSB Exact
    83 15.9 749 19.8 JSB Exact
    84 15.9 746 19.7 JSB Exact
    85 15.9 738 19.3 JSB Exact
    86 15.9 728 18.7 JSB Exact
    87 15.9 728 18.7 JSB Exact
    88 15.9 718 18.2 JSB Exact
    89 15.9 712 17.9 JSB Exact
    90 15.9 707 17.6 JSB Exact
    91 15.9 696 17.1 At 50 BAR
    92 15.9 689 16.8 JSB Exact
    93 15.9 677 16.2 JSB Exact
    94 15.9 669 15.8 JSB Exact
    95 15.9 663 15.5 JSB Exact
    96 15.9 656 15.2 JSB Exact
    97 15.9 647 14.8 JSB Exact
    98 15.9 640 14.5 JSB Exact
    99 15.9 632 14.1 JSB Exact
    100 15.9 626 13.8 JSB Exact
    101 15.9 616 13.4 At 30 BAR
    102 15.9 605 12.9 JSB Exact
    103 15.9 598 12.6 JSB Exact
    104 15.9 589 12.2 JSB Exact
    105 15.9 580 11.9 JSB Exact
    106 15.9 571 11.5 JSB Exact
    107 15.9 555 10.9 JSB Exact
    108 15.9 535 10.1 JSB Exact
    109 15.9 514 9.3 JSB Exact
    110 15.9 501 8.9 JSB Exact
    Bled out
    2879.8 Total FPE

    See how the peak is at shot 41…
    That is the pressure in the tank where the valve is no longer under lock from tank pressure.. So one would note that pressure (or on shot 30 maybe) and only fill to that point, if you don’t want the extra shots and to deal with “valve lock”… by aiming higher at first..

    Ashland Air Rifle Range

  19. $30 scope,

    Take the scope off the rifle and shoot at a target 20 yards away with open sights. Then adjust the sights five clicks to the left and shoot a second group.

    Was there movement when you adjusted the sights?

    Now remount the scope and do the exact same thing. Do it at 20 yards, because much closer and you won’t see any movement. That’s why in my sight-in article I have you move back to 20 yards.


    Finally, please tell me what pellets you are shooting.


  20. Wayne,

    From looking at your numbers I would say your gun came on the power curve at shot 15 and dropped off the curve at shots 50. If I were advising you on how to get the best accuracy at 50 yards, those are the shots I would select for your power curve.

    The downside of your curve is more gradual, so you could argue for including shots out to shot 52, but after that it falls off pretty fast.


  21. Vince,

    That 26 is a modern rifle between the 24 and the 28. For $130 I would say it’s a no-brainer. It’s a now-discontinued Diana (84-92) that is much like the 27, though more powerful because of modern seals. I don’t think it will have the ball-bearing trigger.

    If the condition is good I think it’s a keeper.


  22. B.B.

    Thanks for reading that shot string for me.. but why did you pick shot 15… shot 13 was the same..

    So we try to get the peak shot in the middle of the run? Not the first shot of a run..


  23. Wayne,

    I completely misread your list!

    I’m sorry, but my dyslexia kicked in.

    I meant to pick shot number 32. as the first one and number 50 as the last. That is my real pick for the power curve.

    I’m sorry, but I think the pellet weights threw me off.


  24. BB,

    Thanks for posts like this. You save me and others a lot of money and, more importantly, time. I’m still not ready for the excess baggage and performance profiling others seem to adore in PCP’s, but I’ve got a leg up if I can’t resist the call.

    I still think a regulator would be a “good thing”, even if it had to be replaced every year, not that a little velocity variation is going to affect my antique shooting style:).

  25. B.B. & All,

    To make it clear for me and others, your saying, that small window of shots between 180 bar (about 2,600 lbs.) and 140 bar (about 1,800 lbs.), is for the least loss of POI (point of impact) at 50 yards and beyond.

    For some of us who have power adjusters, (this older Air Arms S410 didn't) and, or shoot at closer distance, could use with very minor adjustment to aiming point, shot 1 to shot 80… 200 bar down to 70 bar, if we are out hunting, far from more air.. or just lazy like me, and want to get to know the rifle better, learning how to aim at different tank pressures, and distance…

    I just don't want folks to get the idea that those many extra shots on both sides of the "sweet spot" are worthless.. at 20 yards, that's maybe 1/2" drop from the peak, shot 41, to shot 80.. and about 1/4" low, on shot 1, under valve lock..
    Some people only take the sweetest of sweet spots, and refill often, some don't.. it's a choice…

    The other factor that Jane points out, and I have before also, is:
    If you have a power adjuster, and the right firing valve, then your first shot can be set, say 880fps (with a AAs410 in this case) and hold that for a while, then maintain it a little longer, by turning the adjuster back up, little by little.. But maybe that's to high tech for us Americans, just the Koreans can figure that out.. Right Jane..

    Ashland Air Rifle Range

  26. B.B. & All,

    I Didn't mean that last part to sound so nasty, but picking a PCP is a hard thing, and I'm passionate about this.. so I'm very sorry…

    Many factors are important.. Tank size, valve, power adjuster, quality of fit of metal to "O" rings, indexing, if a multi-shot, and that's before overall fit and finish and accuracy… then there is noise level..

    That's why that chart is so important for us to make a informed decision…


  27. Wayne,

    My comments were focused on the list you published. I go by velocity – not by pressure. An adjustable power mechanism is another level of complexity that I did not address, except when I adjusted the power for the final string.


  28. B.B.

    Thanks, your right, I was just adding to Janes’ point…

    The power adjuster adds more complexity… and possibility… when you add the needs/desires of the consumer.. it’s hard to find a match.. and then after one tries something, one’s desires/needs can change… more complexity and possibility..

    Again sorry, I’m just kidding about us Americans not figuring it out…


  29. I have a question for anyone out there with a Diana Mod 34 Panther in .22; hopefully someone can spare me some pellet sampler surfing.

    What pellets would you recommend for it?
    I mean this in terms of raw (eliminating the shooter as a factor) precision; or more colloquially: what pellets does the .22 Panther “like” to shoot? I don’t care a whit about velocity or energy or anything like that, just consistency.

    (I’m the one who was asking about the cocking force on the Walther Falcon Hunter a couple days ago; fortunately a friend with a .22 of the rimfire variety has, er, taken care of the raccoon problem and with it obviated my need for an airgun with a lot of shock and awe in its powerplant, price, recoil, marketing etc. There’s really something to be said for the medium strength break barrels that you can get a decent amount of punch from without needing a team of oxen and block and tackle rigging to cock.)

    Thanks in advance to anyone with an answer, and thanks to B.B. for a fantastic blog, and a Happy New Year to All!

  30. Hello B.B. and everyone else!!
    I wish a Happy New Year for everyone… I am back from Dubai and ready to get up to date with the past posts!!! LOL… Congrats to B.B. for achieving the 1000th post!! I bet that you have written about every possible theme related to airguns by now!!! Nice… Happy Holidays to everyone!!!

  31. BB, I looked at the 26 and it seems to be in very decent condition – except that it’s missing its pivot bolt! The bushing is holding the barrel in.

    I did purchase an old R10 at that shop – not as nice as the ’26 but still not bad – the barrel has some noticeable rust and deterioration of the bluing, but the rest of the gun is pretty good. It came with a Bushnell Sportview 4×32 AO scope and a pinned scope stop. I paid $265 for it.

    Turns out that the R10 has a bad piston seal, it was only shooting in the mid 600’s. So I’ll be getting a new one. But the spring is good, and the Rekord trigger works very nicely. And now I’ll be able to compare the REAL Rekord with BAM’s version and see how close they really are.

    BTW – that $265 is the most I ever paid for an airgun in my life! The next closest was about $40 less for a factory refurbished 350.

  32. Vince,

    Then my new years resolution will be to change all that… just ask Kevin!!

    $265! How is PA going to keep this blog going with a spending habit like that? We for sure have to get you into the PCP world, where you can contribute like you should..
    $265… I never heard of such a thing!!

    Happy New Year Again..

  33. Vince,

    Pyramyd AIR has a huge lot of Diana parts left over from the purchase of Airgun Express a few years ago. AGE was the RWS Diana repair center for several years, so these parts are inclusive.

    The pivot bolt you need may be among them.


  34. EJ,

    When I tested the RWS Diana 34 Panther in .177 the best pellet was a 7.9-grain Crosman Premier. And I know from testing other RWS Diana rifles in .22 caliber they like the .22 caliber Premier pellet.

    Read this report:


    I’m referring to the Premier pellets that come in the cardboard box.

    I would also get some 14.3-grain JSB Exact domes. They are good in almost all spring rifles.


  35. Bg-farmer,

    Given that you are one of the sharper tools in the shed, I’m sure you would be able to conclude what the sweet spot is for a rifle relatively quick. It is not only visible on the Chrony but the target also.

    Interestingly the .22 S410 that Wayne test likes a very similar fill as my Webley. The manual states a maximum pressure of 200 bar, but recommends 190. However, I found starting at 180 bar suits the rifle best.

    Then I get 30 shots within a curve that spreads about 40 fps. It makes no difference what the ending pressure is; I simply need 30 pellets counted out.

    Limit yourself to 20 shots and the variance is less than 20fps for the Webley, but I see no real change in POI going to 40fps.

    Besides making your shots more consistent, topping off with a hand pump favors this method. Shoot the rifle almost empty and you’re in for quite the work out.

    The shot strings from some regulated guns I’ve seen vary as little as 5-10 fps, but my Olympic hopes died sometime ago.

    Any thoughts on what the new power source is that B.B. is hinting at?


  36. B.B.

    I think your missing the point with these Korean rifles w/ power wheels. They are meant to be used with the power wheel. I have a Career III 300 & fell into the trap of setting it to the highest setting from a fresh fill & used 2x the air on shots that were not much faster than when starting on "mid" power & using the adjuster.

    My rifle has 14 clicks between high & low. With pellets 14.3 to 21 grains I start on med low power(4 clicks from the lowest setting) on 3100 PSI fill. The 1st 18 shots are @ this setting, then increase 2 clicks after every magazine. I get 48 shots between 995 FPS down to 945 FPS ending @ just over 2000 PSI. For the heavy pellets of over 21 grains I start @ mid power on a 3100 PSI fill. I get 30 shots between 975 FPS down to 937 FPS ending @ 1900 PSI.

    I think you should re-test the rifle using the power wheel how the makers of the rifle intended.

  37. Scott,

    Believe me, I do understand the use of the power wheel on a Korean air rifle. Back in the mid 1990s, I reported getting 100 shots at 30 foot-pounds from my Career 707 by use of the power wheel in The Airgun Letter. And in the Airgun Revue magazine I reported over 100 shot velocities of an Air Arms Shamal air rifle to demonstrate how a power curve is discovered.

    In this report (the one we are commenting on) I shortened that experience to a hypothetical power curve of just a few shots, but that chart above is based on a much more thorough examination I have made in the past.

    But that’s not what I am testing when I test one of these guns. I don’t have the time to spend on any particular model to show off all its quirks and potential. I can only hit the high points before passing on.

    When I tested the Beeman R1 for The Airgun Letter my nine chapters turned into a book (and also into a 13-part blog called Spring Gun Tune for this blog!). Occasionally I do get deeper into certain guns, but I will never be able to devote the time to explore them all as thoroughly as everyone would like.


  38. B.B.,

    I know you do I guess I was hoping you went into it a little bit more(why it's there, how to use it & a example.) Maybe explain the difference between it & shooting a Disco when which has no "stock" power adjuster. I just got the sense after reading the blog that the Infinity wasn't designed well, doesn't have a good power curve or valve. I think with your vast knowledge & decades of experience you could explain using the power wheel vs. not using it so lay men could understand. Lord knows I could have used some of your wisdom on this subject when I got mine. It would have saved me hours of testing & figuring out how to use it…… The manual that comes with it pretty much useless in that regard.


  39. Scott,

    I hope I didn’t sound too crotchety this morning.

    I do appreciate what you say, but here is how I like to address it. Instead of just one particular gun, I like to treat the power wheel by itself. Then, if you have understood me, I have taught you to fish instead of just feeding you one meal. And you will be good for all the guns that have power wheels — or at least all the Korean ones. The AirForce guns don’t fit into the same category.

    Your power wheel comment has made an impression and I guess I need to address it soon. Will you please keep after me — to the point of reminding me that we had this conversation?


  40. B.B.

    Not at all. I understand what you have said & am thankful you provide you're knowledge to everyone. I know you're a busy man & I will send you reminders of our conversation as you requested.

    Respectfully & Happy New Year!

  41. BB,

    If for example, I found my power curve to be at 2600 to 2000 psi, how do I charge from a scuba tank with 3100 psi in it? Just some delicate slow opening of the tank valve while watching the gauge on the scuba adapter?


  42. Dave,

    Not really. CO2 regulates its pressure according to the ambient temperature. It evaporates whenever the gas pressure drops below a certain point that is determined by the temperature. You don’t compress CO2; you chill or or heat it.

    As CO2 is used, it maintains constant pressure because liquid is always evaporating to gas. When the liquid is gone, the gas pressure starts dropping and doesn’t recover.

    Is that explanation clear?


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