By B.B. Pelletier
I received the following question posted as a comment to my May 18 posting, What about Eun Jin pellets? I thought this question deserved a better answer than just a few lines in the comment section, so here it is.
I keep noticing the reference to foot-pounds of [energy] when talking about the force needed for certain ammo. All airguns I read about are usually rated in muzzle f.p.s., or I see a reference to calculating foot-pounds with a particular round.
Do airguns have an “unloaded” foot-pounds-of-pressure [rating] to go by?
I ask because I purchased a Winchester 1000B from Pyramyd Air, and I cannot find a reference to its foot-pounds. Wonderful weapon, by the way.
The foot-pounds of energy that an airgun is capable of generating is related to its muzzle velocity in this way: muzzle velocity X the weight of the projectile = muzzle energy. There’s more to the formula than that, and it has been addressed in Tom Gaylord’s article Airgun formulas and other neat stuff – How to calculate foot-pounds and velocity.
Your air rifle shoots pellets of different weights at different velocities. So it delivers different muzzle energy as the weight of the pellet and its initial velocity changes.
Airguns have a RANGE of muzzle energy
A gun doesn’t just have one muzzle energy rating. It has a range of energy produced with different pellets. An “unloaded” energy rating for any airgun would take into account the expected range from the lightest to heaviest pellet.
Some pellets are too large for the bore and don’t go as fast as their weight would indicate, while others are too small and don’t seal well, resulting in velocity lower than expected. So, instead of a clean graph of energy that changes with the weight of the pellet, we get a graph that has a few surprises in it.
Let’s plug in some numbers and see what happens. On your own Winchester 1000B, let’s say you’re getting 713 f.p.s. with 10.6-grain Beeman Kodiaks. The energy calculator in the article says that would give you 11.97 foot-pounds of muzzle energy. The lightweight RWS Hobby pellet that weighs 7 grains would have to go 855.17 f.p.s. to match that energy, but when you shoot them in your gun, low and behold, they average 901 f.p.s. That’s an energy of 12.62 foot-pounds.
Speed up with synthetic pellets
If you want to shoot even faster, try the Hyper velocity lead-free sabot pellets, type 2 in your gun. At 5.9 grains, you might expect them to go 950 f.p.s., but the plastic skirt has such a low coefficient of friction that they actually go 1,011 f.p.s.! Wow! According to the energy calculator in the article, you’re getting 13.39 foot-pounds!
The bottom line
What we’ve seen in this hypothetical experiment is that your Winchester 1000B air rifle has an energy spread of 11.97 foot-pounds to 13.39 foot-pounds. No airgun has a single muzzle energy or velocity, but each possesses a range of energy and velocity depending on the pellet used.
I used the velocity provided by the manufacturer (1,000 f.p.s.). But since I don’t have your rifle to test, I don’t know how exact that is. My velocity figures for the pellets mentioned are in the ballpark for rifles with the Winchester 1000B’s power range. For actual figures, chronograph your gun with each pellet.