Airgun power with heavy and light pellets

by B.B. Pelletier

We received a lot of comments to last Friday’s post, Why foot-pounds is the most meaningful airgun power rating. One of them was a question from “cold shooter” about something I said in that post: “Please explain why a CO2 pistol would prefer or gain more energy from a heavy weight pellet.” The full statement I made went something like this: “Spring-air guns are more efficient (have more power) with lightweight pellets, while pneumatics and CO2 guns do better with heavy pellets.” Today, we’ll examine this phenomenon.

First, a new book
Trust me, this book is very much related to this discussion. The Practical Guide to Man-Powered Bullets by Richard Middleton has just been published. It’s an excellent discussion of energy transfer, momentum and the design of catapults, crossbows, bullet-bows and airguns. I think this book clarifies the spring-air versus pneumatic question quite well. It’s related to energy transfer.


If you want to understand airguns better, this new book provides many excellent discussions on energy, momentum and the ballistics of airguns.

To acceleration, time is everything!
One of our readers was the first to explain this in the comments to the same posting where the question was asked. He said, “A quick answer to cold shooter’s question. Heavier pellets stay in the barrel longer, which allows the released CO2 gas more time to expand and transfer more thermal energy into kinetic energy.” To simplify that a bit, the more time the gas has to push on the pellet, the faster it will go!

Spring-air guns are quick!
A modern spring-piston airgun, like the Beeman R11 MkII generates power when a steel piston is rapidly shoved forward by a coiled steel spring. The piston compresses the air in front of it, shoving it through a tunnel called a transfer port, where it travels to the breech of the barrel. If a pellet is in the breech, the air is stopped and cannot move forward, so the air pressure builds instead. An immovable pellet on one end and a piston compressing air on the other causes the air pressure to rise quickly in the transfer port. When the pressure reaches a certain point, the tiny lead pellet can no longer restrain it, so the air shoves the pellet up the barrel.

Springers just puff!
While the air compressed by the piston is at high pressure, there isn’t very much of it. Once the pellet starts moving, the pressure starts dropping as the volume of the bore behind it increases. By the time the pellet has travelled 9″ to 11″ up the bore, the air is almost back to normal pressure, so it stops shoving the pellet. By this time, the pellet is traveling as fast as it will ever go. Since the time of acceleration is very short, lightweight pellets tend to go much faster than heavyweights. They resist the air pressure less so they start moving sooner, affording more time to accelerate.

While gas guns blast!
Both pneumatics and CO2 guns use a greater volume of gas than the spring gun generates. In the case of CO2, it’s not at a very high pressure (900 psi, compared to about 2,000 psi in a spring gun) but there is so much more of it that it keeps on pushing far longer than the tiny puff from the spring gun. As long as the barrel is long enough to put the pressure to good use, both pneumatics and CO2 guns will accelerate heavy pellets to higher velocities than spring guns can, and that’s where they get their extra power. If you were to cut the barrel of a pneumatic very short, you would also cut the power. The AirForce Talon SS provides an excellent example of this. With the standard 12″ barrel, the gun gets 830-850 f.p.s. with .22 caliber Crosman Premiers. When you install an optional 24″ barrel on the gun, the velocity of that pellet jumps to just over 1,000 f.p.s. – without changing anything else!

However, the Talon SS still generates more power with its 12″ barrel with heavy pellets than it does with light ones (26 foot-pounds with Beeman Kodiaks versus 23 with Crosman Premiers), because the pellet is accelerated all the way to the end of the barrel.

CO2 is even more dramatic!
CO2 is a gas that changes pressure with temperature, so if the gun you shoot is relatively warm, the gas maintains its pressure much longer. Also, the large size of the CO2 molecule means the valve has to remain open longer, so fresh gas is replenishing the supply in the barrel. The results can be dramatic! A Farco air shotgun, for example, can generate 100 foot-pounds on a warm day, due to a very long barrel and CO2. And, the Farco provides the perfect example of light versus heavy pellets. A 120-grain .433 ball produced 65 foot-pounds in my gun, while a 245-grain load of shot made 105 foot-pounds on the same day. It doesn’t get more dramatic than that!

This is a good experiment for your new chronograph. You will find some anomalies, but in general, this rule will hold true.

42 thoughts on “Airgun power with heavy and light pellets

  1. Sir. I have a question concerning barrels. Why are barrels on the Sheridan and benjamin pneumatic rifles made of brass but not the barrels of most co2 guns, since it won’t rust?


  2. Brass barrels,

    Well, that’s why both the Benjamin and the Sheridan rifles cost a little more. Brass it ideal for multi-pump pneumatics and CO2 guns, as you note, but it does cost a little more. Every dollar the manufacturer adds to anything costs the consumer five dollars, so they watch the pennies carefully.

    Now when it comes to PCP guns, they use dry air, so the problem of condensation is reduced.

    B.B.


  3. I think it has more to do with weight and performance than cost. Brass is not only heavier than steel, but it is also weaker, requiring very thick barrels. That makes for a impractical size and weight for the barrel. Benjamin and Sheridan guns overcame this by attaching the barrel to the main body tube, giving the barrel the strenght and rigidity it needed for acceptable performance.


  4. Hi BB,

    Sorry for the off-topic, but since we’re talking Benjamin-Sheridan’s, can the 392 or other pneumatic rifle/pistol be dry-fired without harm? Just got a new one for Christmas.

    Thanks!


  5. B.B.,

    Another detour. Williams peep sight (w/nothing but screw adjustments). Where can I find written instructions on making windage and elevation adjustments? Great posts.

    OWO


  6. B.B.

    I am confused on how you explain lighter pellets in springers “… resist the air pressure less so they start moving sooner, affording more time to accelerate.” I seem to me that if the move sooner, they would get out of the acceleration zone sooner and have less energy. Maybe I am missing something. Could you clarify? Thanks.


  7. I may not be explaining it correctly. Perhaps, due to the light weight, the pellet accelerates to a higher proportional velocity than a heavier pellet can, owing to the small volume of compressed air made by the spring-piston powerplant.

    It may be more like a feather hit by a small puff of air. The same air wouldn’t affect a softball, but if it lasted longer it might, and the softball would eventually have much more energy than the feather, regardless of how fast the feather got going.

    What I do know for certain is the relationship works as described.

    B.B.


  8. Thanks for the first two items because they both fit my question. I’m brand new to airgunning, and just bought a Gamo Shadow 1000. Reading others info, they talk about slowing down the f.p.s. to about 900 to escape the problem with approaching the speed of sound. They suggest using a heavier pellet to accomplish that. The other side of the coin, I understand, is to use the lighter pellet in a spring gun. So, what weight pellet is best for the rifle I bought?
    And, is a .177 pellet realy not suitable for hunting? Thanks for your advice.

    Highlander


  9. Highlander,

    No, a .177 pellet IS suitable for hunting, but it has some drawbacks. The greatest is that it often over-penetrates without tranferring much energy to the animal. The animal then runs away and suffers. A .22 pellet delivers more of a smack when it hits.

    That said, your new Shadow 1000 is fine for hunting. Just shoot for the most vital spoit, which usually means the brain.

    As for pellets, go for accuracy over everything else. Start with the JSB Exact heavy,the Beeman Kodiak and the Beeman Field Target specials. You migh also try Gamo’s Magnum Pointed pellets. There ought to be a good one in that group.

    B.B.


  10. B.B.

    If you don’t mind, I can attempt to answer the other reader’s question on why lighter pellets absorbs more energy from springers. Here it goes.

    In a springer, consider the acceleration zone to be a fixed distance (ie. 10 inches into the barrel like B.B. said) regardless light or heavy pellet (if you want to know why, I can explain it later in another post). In a perfect world where there’s no friction, the light and heavy pellets would have the same amount of kinetic energy right at the 10 inch mark. In fact, we can just use this model within the 10-inch acceleration zone because the energy transferred to the pellets is a lot greater than the energy lost due to friction in these 10 inches. With this in mind, light and heavy pellets have ROUGHLY the same amount of energy right at the 10 inch mark in a springer. Past the 10 inch zone, it’s a different story. There’s no more energy to transfer into the pellets. All we have is energy loss due to friction with the barrel until the muzzle. Heavier pellets intrinsically create more friction and thus lose more energy than lighter pellets. This is why at the muzzle lighter pellets still contain more energy than heavier ones. Hope this helps…


  11. BB,

    In your response to Highlander’s question on pellet weight you listed Beeman Kodiaks as a good choice for his air gun.

    My question on this is: is the shadow 1000 considerably different than the cfx in regards to pellet propulsion? What would make the kodiaks too heavy for the cfx ( as was a partial answer to a question I had over another blog conserning siting in a scope ), and not too heavy for the shadow 1000?

    I would think that the two Gamo’s would be the same.

    dsw


  12. BB,

    Forgot to mention that this was an excellent topic and clears alot up for me as to the gas vs. high pressure guns vs. springers. all made good sense, like the relationship of horse power and torque in an engine.

    How does the noise factor play out? I know springers cant be altered for lower sound levels effectively, what about the others?

    dsw


  13. DSW,Today I got my CF-X and in the mini catalog it says it brings a 2-7x32mm scope and it came with a 4x32mm.Whats wrong and what should I do.BB you can also help me please.



  14. CFX,

    weather you ordered a combo or not I guess is irrelevant, sorry.

    Let’s look at your delivery… is it what you ordered?

    What do you plan to do with it? Long range target? General plinking? Shoot pesty birds?

    Is the scope a Leapers? You know Leapers has a 4×32 Bug Buster that I would love to own! Is that what it is?

    Have you used a scope much? A 4×32 is a great all around scope without the time consuming adjusting. I have lost many a shot on getting the target sited on an adjustable scope.

    dsw


  15. BB

    I am confused, I know you said the rws 48 in 22 works better with a heavy pellet but does this post contradict what you said before

    Thanks


  16. B.B.,
    As all the others have said before me, you are doing a wonderful job here. I hope this blog continues for a long, long time.
    The discussion about springers vs. CO2 brings up another question. By me a good winter day is maybe +20ºF. How much power loss am I experiencing by shooting my C02 guns now as opposed to shooting in warmer weather, say 50º?


  17. dsw,

    I don’t remember what I said or the context in which it was meant, but the Kodiak is a good pellet for the CF-X.

    I do know that I was laboring for a long time under the false belief that the CF-X used some kind of magazine, instead of a rotary breech. Perhaps that was what made me say what I did.

    At a rating of 1,000 f.p.s., the CF-X has all the power needed to shoot the Kodiak pellet well.

    B.B.


  18. dsw,

    Regarding airgun powerplants and noise, I have already touched on this subject in several posts, but this is too good to pass up.

    Watch for a more detailed answer next week.

    B.B.


  19. CF-X scope guy,

    It would really help if you used a handle (nickname) so we can communicate through all the other comments.

    As for your problem, if you did order a CF-X combo then it should have had the BSA 2-7 variable scope, as advertised. Get on the phone to Pyramyd Air and tell them the problem.

    Good luck,

    B.B.


  20. RWS 48 guy,

    No, what I said about light versus heavy pellets in a spring gun does not contradict the fact that any .22 airgun is going to be about 20 percent more efficient than the same airgun in .177.

    If you are still confused, let me know and I’ll make it a blog topic.

    B.B.


  21. Reader from Frostbite Falls,

    If a good winter day is +20 and you consider 50 degrees to be warm, I know you must be living up in Bullwinkle country!

    CO2 guns are not really effective below 50 degrees, and they really don’t even like it that cold! CO2 wants to work on an 80 degree day, so the gun will warm back up after the shot. At 20 degrees, you have lost about 30-40 percent of your power (that you had at 70 degrees), I would think. And your gun will never recover. It will get colder and colder until it almost doesn’t work, if you fire rapidly.

    B.B.



  22. Hernan,

    Well, getting a nickname is pretty simple. All it takes is a check for $50, made out to me. There is a form to fill out, but I’ll waive that for you.

    Or, you could just call yourself Hernan, or CFX or something like that. I don’t like shortcutting the system, but people do it all the time.

    That was a joke,

    B.B.




  23. BB

    On dicember 29 post you called told me that I shoul be CF-X guy so I want to correct that my post above says only cf-x so from now on youll now me{Hernan} as CF-X guy.

    Thanks BB your great and youve help me a lot since im new to airgunning.By the way I got my GAMO CF-X and its great.Could you do a post on it?Id really apreciate it.Scince I really dont understand some of the stuff like the rotary breach.BB I have not shot the cf-x yet cause ive only had it for a day and the manual is not easy to understand.So please help me and make a post for The CF-X.Thanks BB.Keep up the good work.

    CF-X guy



  24. B.B.,
    It is really not Frostbite Falls. It is a small piece of heaven called Talkeetna, Alaska!
    would you recommend a spring pistol for removing squirrels?
    thanks!
    cold shooter



  25. CF-X guy,

    Okay, I’ll do the CF-X. I have not shot one, but I have shot the very similar BSA Superstar, which also has a rotary breech. Gamo owns BSA and they probably got the rotary breech from them. They also got the Stutzen from BSA, so there is a lot of transfer going on.

    I will need your help, though. After I write about the gun(s), I want you to post your impressions of your CF-X. I will tell you what I want you to tell us about.

    Deal?

    B.B.


  26. BB,

    Thats a deal.Ill go sight in the scope today and will tell you in the post what were the results and every detail.Thanks BB you are the best andI really mean it.

    CF-X guy.


  27. Hello BB,
    Here is a little info on the CF-X. Have been shooting mine for over 1 year, about 1k rounds thru it. Overall nicely built gun. Fit and finish is quite nice for the price. It’s heavier than it looks, and probably makes it easier to shoot. Synthetic stock is quite durable, and is sized for an adult shooter. Mine is a bit hold sensitive. The Trigger has smoothed out nicely, consistent and predictable. Vibration has quieted down too.
    I have the “combo” with 2-7xAO BSA scope. I did not use the scope stop, and rings that came with it. I choose to use B-square medium Airsport rings(these have an integral scope stop pin built into the ring base, which will nicely fit into the stop pin hole on the receiver rail). Much cleaner look than the separate scope stop. Scope is very nice, compares to much more expensive ones I own. Even comes with screw in aluminum lens covers! I might even buy another for one of my rimfires.

    I have found this rifle very accurate, ragged 3/8-1/2 inch groups at 10 meters. It likes both weights of Crosman premiers. 10.5gr average 742fps, and 7.9gr average 887fps. Beeman Kodiaks @ 10.5gr and 782fps aren’t bad either. The fastest pellets I have shot are Daisy Pointed 7.3gr at average 938fps. The best wadcutter pellet is RWS Meisters 8.2gr and 856fps. The most accurate of these pellets is probably the Heavy Premier.
    Yes the breech is “rotary”. You MUST, I repeat MUST, cock the gun before trying to open (rotate) the breech. Forcing the breech will cut the seals and lead to repairs. Loading is really pretty easy, even with my large fingers. I point the muzzle down at about 45 degrees, drop the pellet onto the groove in the breech, it slides into the barrel. Some pellets need a little press with a fingernail to flush into the barrel. Rotate closed and go.
    I don’t like the safety. The safety lever is inside the trigger guard! I don’t like my finger in the trigger guard till I’m ready to shoot. Too easy to release safety and fiddle with trigger unintentionally. I would prefer a crossbolt safety instead. That’s my only negative comment on the CF-X.
    It’s a great shooter! Hope this helps with your report. Sorry for the long post. You can Quote me if you wish.

    JB


  28. JB,

    Have you really gotten a 40fps difference between the Premiers and the Kodiaks?

    Interesting, and thanks for the info. I have been assuming that the 1000fps was accurate and measured with a 6.9 pellet. That puts my math off a bit.

    dsw


  29. JB,

    What timing! I’m posting the CF-X review tomorrow and it’s amazing how close I came. Apparently, the CF-X IS a lot like the BSA Superstar and the parts that are different, like the trigger, are classic Gamo.

    Thanks, and I will quote you.

    B.B.


  30. how can i increase the power of my airgun,that is a gamo maxima ’22 cal.?what type of lubricant should i use for my pellets to increase their velocity if i want to avoid any dieseling in the barrel that could destroy the internals of my air rifle?


  31. B.B.

    When you say pneumatics do better with heavy pellets, do you mean precharged pneumatics or single pump pneumatics, or both? Thanks.


  32. I guess that does require an explanation! I meant precharged and MULTI-pumps. I never even thought about single-strokes. They might do marginally better with heavy pellets TO A LIMIT, but because the stored air charge is so small, I only use lighter pellets in them.

    B.B.


  33. theoretically couldn’t you achieve the same muzzle energy of a rifle with a pistol using the same size charge of gas by using a much heavier pellet? How long does a barrel have to be to use the full energy of co2?


  34. dougal,

    Both CO2 and air need a certain length of barrel to achieve velocity. It also depends on caliber. For a .177 CO2 gun it’s around 16 inches. For a .177 pneumatic it’s around 28 inches.

    Those numbers are not exact.

    B.B.


  35. B.B

    Wouldn't the time it takes for a pellet to stop being pushed by air in a spring powered airgun barrel be dependent on the volume of air that was compressed? For example, if a airgun has a compression chamber that holds 6 cubic inches of air is actually pushing on the pellet for the first 10 inches up the barrel wouldnt a airgun that had a 12 cubic inch compression chamber push on the pellet for the first 20 inches of barrel? Thanks a lot B.B.


  36. Michael,

    But the numbers you used in your hypothetical example are far beyond what a real spring-piston gun has available. Spring-piston guns typically develop 25 percent or less of the power stored by the spring.

    B.B.


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