Why foot-pounds is the most meaningful airgun power rating

by B.B. Pelletier

I posted an article on foot-pounds back on July 15. A fellow calling himself “nordattack” took issue with what I said. I told him I would need to think about what he had said, then make my reply. Instead, I forgot to do anything about it. On December 21 an anonymous poster very clearly made the argument I should have made, so I’ll give the credit for this post to whoever that was. Here is why I believe foot-pounds is the MOST ACCURATE method to rate power in an airgun.

nordattack proved my point!
nordattack said, “If we are simply told an airgun has 25 foot pounds at the muzzle, again without knowing the weight of the pellet, we are clueless. I mean it could be a 900 caliber pellet going 5 feet per second!” No sir, we are not clueless. I can tell you A LOT of things about an airgun that produces 25 foot-pounds at the muzzle. Here goes!

No manufacturer is going to show their own gun in a bad light.
We know that a spring gun almost always generates greater power with light pellets, while a pneumatic or CO2 gun does just the reverse. So, depending on the powerplant, we can at least determine the range of pellet weights used for testing, if not the exact pellet. If the gun in question is a Diana RWS 350 Magnum, which is a spring gun, and .177 caliber, it has to shoot 6.9-grain Hobby pellets at 1,277 f.p.s. to generate 25 foot-pounds. Since that’s too fast for that rifle (it tops out at about 1,150 f.p.s. in .177), the stated energy is probably false. In .177, an RWS 350 Magnum probably produces a little more than 20 foot-pounds (6.9-grain pellet moving 1,150 f.p.s. at the muzzle).

If, however, the spring rifle happens to be a .22 caliber 350 Magnum, then to produce 25 foot-pounds it would have to shoot 11.9-grain .22-caliber Hobby pellets at 972 f.p.s., which IS believable! And, if it does that, it will probably also shoot 21-grain .22-caliber Kodiaks at about 700 f.p.s., which generates 22.85 foot-pounds. Can I rely on that number? Not exactly, but I can be reasonably certain that the rifle won’t shoot .22 Kodiaks as fast as 775 f.p.s., but that it will be faster than 675 f.p.s. I arrived in that ballpark from the stated foot-pounds, even though I know that, to get those foot-pounds, the manufacturer had to shoot the lightest pellet it could find.

How do you know spring guns get more energy from light pellets, while pneumatics get more energy from heavy pellets?
Simple! I tested several different pellets and observed the results. You can do the same. While this phenomenon is not 100 percent guaranteed, it will turn out that way most of the time.

Knowing the muzzle energy tells you a lot about the airgun!
If you tell me a certain airgun produces 30 foot-pounds in .22 caliber, I know from experience that the gun has enough power to shoot 28-grain Eun Jin pellets. If it’s a spring gun, I know it was tested with light pellets and will only generate about 25 foot-pounds with Eun Jins. Going to the energy calculator on the Pyramyd Air website, I can convert that to a muzzle velocity of 634 f.p.s. If the gun is a PCP, I know that it was probably tested with Eun Jins to get the stated 30 foot-pounds. That’s 694 f.p.s. And, I know that it will get less energy with Kodiaks, perhaps 27 foot-pounds or so, which turns out to be 761 f.p.s. Those numbers are not exact, but they are in the ballpark, and that’s what the energy level of airguns can tell me.

Velocity, alone, has much less meaning
Telling me the muzzle velocity alone is like saying, “Here’s a partial score – Cleveland 11….” You didn’t tell me who they were playing nor what kind of game they were playing. I remember reading about a Beeman P1 that some guy converted to shoot 1/8-inch ball bearings, just so he would get 800 f.p.s. The converted gun was a smoothbore, so the accuracy was lost, but he had that magic number! Velocity by itself is meaningless.

Muzzle energy tells the whole story!
Muzzle energy, however, is the combination of both velocity and the weight of the projectile. Because we know the general span of pellet weights for each caliber, muzzle energy clues us into BOTH pellet weight and velocity at the same time. Knowing the performance of the various powerplants (i.e., spring guns favor light pellets, PCPs and CO2 guns like heavy pellets) allows us to quickly determine the gun’s performance range with all types of ammunition.

24 thoughts on “Why foot-pounds is the most meaningful airgun power rating

  1. Good post. I agree that the ft-lb rating is the most useful number for an airgun. But I guess it’s only useful if you know how the math works. Apparently most people don’t…

    Could you do a review on POWERLINE 953 TargetPro? I heard a lot about how accurate it is but not sure if it’s true. Thanks.


  2. Just currious. Does this mean that when using a monster rifle like the Webley Patriot in .25 cal, the 21g Diana domed will generate more foot-pounds than the 36.6g Eun Jin pellets?


  3. Poweerline 953,

    I have not actually shot one of these yet. All my experience has been with the 853. But I know some people at Daisy I can ask. The big concern is accuracy, right?

    B.B.





  4. Hi BB,
    Sorry this question isn’t about the current posting, but I hope you would be kind enough to answer anyway. I was wondering about your opinion on at what distance should a scope on a Benjamin 392 be zeroed?Thanks for writting theese wonderful blogs, and answering all of the readers questions. Keep up the good work!

    Jason


  5. B.B.
    Another unrelated post. I have been working on a Crosman 1077 and discovered that the CO2 cartridge seal is cracked. I need to replace it since my jury rigged part does not hold too well. Any suggestions about who might carry parts for this gun?
    CWI


  6. FORGIVE ME. I guess i am getting duller with the passing of time. please explain why a co2 pistol would prefer or gain more energy from a heavy weight pellet.


  7. cold shooter,

    You’re not gettig dull. This is a fact that’s not understood by a great many shooters.

    I simply put it into my posting without an explanation, but I will explain it in the coming week.

    B.B.



  8. a quick answer to cold shooter’s question. Heavier pellets stays in the barrel longer, which allows the released co2 gas more time to expand and transfer more thermal energy into kinetic energy.



  9. Here in the U.S. we know the 95 as the Beeman R9, I believe. An R9 will produce something around 16-17 foot-pounds, so an FAC HW 95 should do the same, I think. Weihrauch lists it at about 800 f.p.s., which would have been obtained with a Hobby pellet, I would guess, and the energy calculator on this website says that is 16.92 foot-pounds.

    So there’s the answer in a nutshell!

    Merry Christmas,

    B.B.


  10. BB, and Y’all, thanks for the informative blogs! I’m not sure how to post or navigate around here yet but I really enjoy what you’ve done and the info is never ending, love it!

    Happy Holidays, and keep up the great stuff!

    dsw


  11. IN REGARDS TO THE QUESTION OF HOW TO SEAL THE CO2 LEAK ON THE CROSMAN 1077. I’VE USED THE WASHER FROM ALUMINUM ROOFING NAILS. THESE ARE THE NAILS USED FOR INSTALLING FIBERGLASS PANELS. I LUBRICATE THE WASHER WITH SILICONE BEFORE USING.
    THIS MAY SOUND ODD BUT IT HAS WORKED FOR ME FOR YEARS ON AN OLD CROSMAN BUILT IN THE 50′S



  12. BB,

    I’ve been chewing on this article and the posts following and am wondering…

    How is the measure of energy in foot-pounds at the muzzle on a spring piston powered air rifle shooting a light pellet an advantage over a medium weight or heavy pellet at the point of impact? Isn’t the heavier (within reason) pellet going to transfer more energy to the target?

    I would have thought that a 1250fps .177 launching heavy pellets would be the most effective at the target , but the point of springers being “short of breath” due to the limited amount of air involved makes me rethink.

    Hmmm

    dsw


  13. dsw,

    First, there are no spring rifles shooting heavy pellets at 1,250 f.p.s. They would be VERY effective, but they don’t exist. To get that velocity from a springer requires a Hobby pellet weighing 6.9 grains. The same gun shooting Kodiaks is going to be down around 900-950 f.p.s. The only gun I have ever seen do this was the Gamo Hurricane 1250.

    As far as energy transfer is concerned, you just earned youself another one or two postings, to allow me to answer in detail.

    Thanks for a really good question,

    B.B.


  14. BB,

    I understand heavier pellets lower muzzle velocity, I’m sure you know what I meant buy your response.

    Even though a heavy pellet is going slower it has more energy when it hits than a lighter pellet at a much faster speed when it hits.

    Anyway, my point to this is how does the “short breath” play out? That was something I totally overlooked.

    The crazy thing is all I wanted to do was replace my Crosman 760! After buying a Gamo CFX, a month or so deciding on the right scope, two or three months on mounts, and a couple hours blogging, a laugh because I just bought a Special Edition Crosman 760 before they ran out!!!!

    looking forward to upcomming related posts,

    dsw


  15. Hi,

    Im curious as to how much fpe a Benjamin
    392 has? I’ve tried looking for the anwser but just can’t find it! If anybody could help that would be great thanks!

    Tyler


  16. Tyler,

    An easy way to find that out is to look at the Sheridan Blue Streak, which is very close to the same rifle in .20 caliber. It gets about 675 f.p.s. with a 14.3-grain pellet, give or take. So that’s what a 392 will get with the same weight pellet and eight pumps of air.

    B.B.


  17. Tyler,

    I’m sorry. I missed what you said. You asked about energy, not velocity. By going to the Pyramyd Air energy converter in the article about muzzle energy,

    http://pyramydair.com/site/articles/formulas/

    I plugged in 14.3 and 675 f.p.s. and got an energy of 14.47 foot-pounds. By the way, at a velocity of 671 f.p.s., all objects develop the same energy in foot-pounds as they weigh in grains!

    B.B.


  18. Light pellets maybe fine to produce "muzzle energy" but at usual hunting range of between 25-50 yards they deliver LESS energy to the target in general because they slow down faster.
    So I don't particularly care what the FPE is at the muzzle.


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