N/A Muzzle energy varies with pellet weight, WHY?

[Scotchmo]

That number can be found to be different in many places, sometimes rounding differences, one time long ago it changed with a more accurated definition of gravity. The number is basically 7000 grams squared * acceleration of gravity in ft/second squared. It doesn't matter, anything close doesn't change anything unless looking out to many decimal places.

What would the muzzle energy formula be if it were calculated in deep space, where there is no gravity?

Ok. I already know the answer. And the actual muzzle energy is the same on the earth as it is in space, and gravity has nothing to do with it. If you use weight and the estimated acceleration of gravity, you can introduce other errors. Use mass instead as that’s what the kinetic energy equation calls for. I convinced AAFTA to use 450,436 because that is the more correct (though rounded down) value.

 

[Mycapt65]

I can't add to the excellent notes above - and this is a detour from the OP's question - but I would note that heavier pellets tend to have better ballistic coefficients, and thus retain velocity better.

In other words, energy at the muzzle is not the whole story. The heavier pellet that starts with less energy, often delivers more downrange than the lighter one.

While theoretically that's true, a heavy pellet's BC seldom makes up for the lower muzzle energy in the distances springers are shot. My R1 was 17 fpe with a 8.64 FTT and 12.5 FPE with a 10.65 Barracuda. The distance required for the two to even hit the same energy I'm sure would be well past the practical range of the rifle. This is a drastic case example but typically BC improvements within a caliber are slight and don't make much difference at typical airgun ranges. Unless you compare extremes like Hobby wadcutters to JSB heavies. In that case you'd be right but you might still have to go 30 yards before the heavies pass the hobbies noticeably.

Energy, drift and velocity retention improvements from an improved BC typically need long distances to reveal themselves. Longer than most springers are shot.

be well Mike
Ron

 

[JEFFPPC]

Well Ron pick your poison. If want simplicity but with a learning sure you want s Springer. Out to 50 yds in good conditions by a competent shoot they will pretty much stay with a PCP. But if you want to shoot farther, shoot larger calibers, and as far as shooting technique not really much to learn you will enjoy a PCP. Now all the theory in the world will not have you shooting x's, that takes practice.Take those graphs or charts, put a dot in the middle, and start shooting at it. Have fun.

 

[MDriskill]

While theoretically that's true, a heavy pellet's BC seldom makes up for the lower muzzle energy in the distances springers are shot. My R1 was 17 fpe with a 8.64 FTT and 12.5 FPE with a 10.65 Barracuda. The distance required for the two to even hit the same energy I'm sure would be well past the practical range of the rifle. This is a drastic case example but typically BC improvements within a caliber are slight and don't make much difference at typical airgun ranges. Unless you compare extremes like Hobby wadcutters to JSB heavies. In that case you'd be right but you might still have to go 30 yards before the heavies pass the hobbies noticeably.

Energy, drift and velocity retention improvements from an improved BC typically need long distances to reveal themselves. Longer than most springers are shot.

be well Mike
Ron

Thanks Ron - very interesting as always!

I should have offered the caveat that I mostly shoot lower-powered old-timey springers and light-ish ammo, so my range of experience with ballistic numbers is well below many of the folks here. 17.0 vs.12.5 FPE is quite an extreme disparity in energy output, never approached that percentage with anything that I have.

As an example, I recently ran five, 15-shot strings with different pellets through a HW 50S from the '70's. The weights ran from 6.9 to 8.4 gr, and the energy from 7.25 to 7.99 FPE. Not enuff diff to keep this old collector/plinker nerd up at night!

A more accurate general statement is that heavier pellets tend to shed energy with distance at a slower rate that light ones. Whether the former passes the latter at some point is a separate question, ha.

 

[Mycapt65]

Thanks Ron - very interesting as always!

I should have offered the caveat that I mostly shoot lower-powered old-timey springers and light-ish ammo, so my range of experience with ballistic numbers is well below many of the folks here. 17.0 vs. 12.5 FPE is quite an extreme disparity in energy output, never approached that percentage with anything that I have.

As an example, I recently ran five, 15-shot strings with different pellets through a HW 50S from the '70's. The weights ran from 6.9 to 8.4 gr, and the energy from 7.25 to 7.99 FPE. Not enuff diff to keep this old collector/plinker nerd up at night!

No problem Mike. You know I love you. The R1s disparity is somewhat extreme but not far from common losses when increasing weight and or using tighter fitting pellets. Here's a more typical example. My Hw30s shoot 7.33 at 715 fps (8.32 fpe), JSB 8.44 at 645fps (7.79 fpe) and the very slightly heavier H&N FTT 8.64 at 615 fps (7.25 fpe). The latter never make good power in my 177 Weihrauchs because the tighter fit and lead alloy. The FTT are very accurate but the power penalty is a little too much for my taste.

Let's compare with BC data from personal testing between muzzle and 30 yards.
Red= 7.33 @ 0.018 BC
Blue =8.44 @ 0.021 BC

Here you see it takes 30 yards for the 8.44 to catch the up with the energy of the 7.33 and 40 yards before it passes it. Still you'd be correct in your earlier post.

Here you see the POI on 7.33 is always higher.

Here you see there's less wind drift with 8.44s.

In this real world example the better BC of the 8.44s doesn't really take affect until 40 yards. Most people shoot these rifles inside of that. I charted it out to 100 yards because I'll plink soda cans at 100 yards. At that distance I'll use the 8.44s if there's any wind.

Give me a call I'd like to talk to you about going to that big airgun show in NC?

Ron

 

[G-Man]

I stand corrected, in a perfect system my response would have been valid...lot's of info out there on the intarwebs...

Why do heavier pellets tend to shoot at higher energy than lighter pellets? - Airguns & Guns Forum

Why do heavier pellets tend to shoot at higher energy than lighter pellets?, Air guns, Airgun Forum

www.gatewaytoairguns.org

Thanks for keeping me honest!

 

[Berserkeley Mike]

Thanks for keeping me honest!

Thanks for being honest!

Here is another bit that may be true: as I understand it, some PCPs (such as my Airforce) use the decrease in pressure as the pellet starts to move, to help shut the valve. So a heavier pellet with more inertia can keep the valve open a bit longer, allowing more energy.

Another bit, if one looks at the OP's graphs, I think even the Pumpmaster showed a slight increase in power up to about 0.7 gram, and then a maybe slight decrease.

And since everyone is showing data, here are results from a Hatsan Mod25 with either a .177 or .22 barrel, driven by either a metal or gas spring, one gun, four configurations. The pellets were non-lead alloy, so the .177s are under 7 grain and .22s are over. My apologies for the non-SI units.
In this particular case the gas ram wasn't as powerful, but note say the 11.7-11.8 pellets, how one showed ~10% more power with the metal spring but the other ~33% more. I note that the ones where the power was relatively high for weight, and the closest between springs, have the softest skirts (Predator GTOs, Winchester MVP). I don't know why the gas ram prefers a particularly soft skirted pellet (if one could even call an alloy pellet "soft").

 

[karl_h]

What would the muzzle energy formula be if it were calculated in deep space, where there is no gravity?

Ok. I already know the answer. And the actual muzzle energy is the same on the earth as it is in space, and gravity has nothing to do with it. If you use weight and the estimated acceleration of gravity, you can introduce other errors. Use mass instead as that’s what the kinetic energy equation calls for. I convinced AAFTA to use 450,436 because that is the more correct (though rounded down) value.

When discussing foot lbs, which is the standard use of muzzle energy in the United States, gravity is needed to calculate, changes mass to weight. But you knew that already so why post what you did.

 

[Deerstalker]

It is because of the way the formula for muzzle energy works. Muzzle Energy (in foot-pounds) = (Bullet Weight in grains * Velocity squared in feet per second) / 450,400. For example, if a 230-grain bullet is traveling at 850 feet per second, the muzzle energy would be (230 * 850^2) / 450,400. So what that mean is if a projectile is lighter or heavier it will have different muzzle energy if traveling at same speed. The reason for speed dropping differently from different guns may be due to many factors including how efficient the air travels from valve to barrel and probable more so by how tight or loose a pellet or slug is in the bore. Just because a gun is .177, 22, .25 does not mean that each barrel will be identical. This is why 2 exact guns in the same caliber may shoot different using the same ammo and velocity.

This may help.

FPS = Feet Per Second, MPS = Meters Per Second, FPE = Foot Pounds of Energy.
To convert to Joules multiply FPE by 1.3558, Joules to FPE multiply by .7376
To convert MPS to FPS, MPS x 3.2808399 = FPS .
To convert FPS to MPS, FPS x .3048 = MPS.
FPE Formula is Pellet weight (gr) x FPS x FPS divided by 450240 or 450436.7.
450240 is 2 x velocity of gravity x 7000, (2 x 32.16 x 7000 = 450240) 450436.7 is 2 x velocity of gravity x 7000, (2 x 32.17405 x 7000 = 450436.7) The constant 450240 or 450436.7 depends on which value you use for the velocity of gravity, (acceleration due to gravity). 32.16 ft/s/s or 32.17405 ft/s/s. There are 7000 grains in one pound. The difference does not matter which ever constant is used for the FPE calculation.

 

[Scotchmo]

When discussing foot lbs, which is the standard use of muzzle energy in the United States, gravity is needed to calculate, changes mass to weight. But you knew that already so why post what you did.

If we were on a planet with 1/2 the gravity of earth, would an airgun’s kinetic energy be 1/2 what it was on earth? Answer: no

Muzzle energy of a projectile is kinetic energy and is not affected by gravity.

I don’t need the acceleration of gravity to calculate kinetic energy. The kinetic energy equation is:

KE = 1/2 * m * v^2

Gravity is not part of the equation. If v is in feet/sec, than m would be in slugs mass. Convert grains to slugs:

https://www.unitconverters.net/weight-and-mass/grain-to-slug.htm

and then plug it into the KE equation. That is the kinetic FPE.

 

[karl_h]

And a slug is what? Let me help you there..... 32.17404 lb, wow, gravity again.... How do you think it is derived. Whenever science talks about weight, it is all based on gravity, full stop. It doesn't matter what units they use. There is no weight without gravity, and standard gravity is 1g. It's why science much rather do everything in mass.

 

[Scotchmo]

And a slug is what? Let me help you there..... 32.17404 lb, wow, gravity again.... How do you think it is derived. Whenever science talks about weight, it is all based on gravity, full stop. It doesn't matter what units they use. There is no weight without gravity, and standard gravity is 1g. It's why science much rather do everything in mass.

Best that you make the distinction between lb weight and lbm. A slug is 32.17405 lbm. There are 7000 grains in a lbm.

7000 x 32.17405‎ = 225,218

There are 225,218 grains in a slug mass.

So, either way you look at, when velocity is in fps and mass is grains, the kinetic energy formula:

1/2 x m x v^2

Becomes:

1/2 x 1/225218 x v^2

Or

v^2/450,436

The instances when we see numbers like 450,240 or 450,249 are when someone treats grains as a weight, and then uses a rounded off, or a slightly incorrect number for gravity to convert grains as a weight to slug mass. Most don’t realize that being a mass, grains can be converted directly, without using gravity.

As I said, gravity is not needed to calculate kinetic energy.

 

[Deerstalker]

Copolit

A slug is a unit of mass primarily used in the U.S. customary system. It's derived from the imperial unit of force, the pound-force (lbf), and is defined as the mass that accelerates by 1 foot per second squared (ft/s²) when a force of 1 pound-force is applied.


In simpler terms: 1 slug = 32.17405 pounds (lbm), based on Earth's standard gravity of approximately 32.17405 feet per second squared (ft/s²). It's a handy unit for physics and engineering when working with force, mass, and acceleration together!

Gemini

A slug is a unit of mass in the British Imperial and United States customary systems of measurement. It is defined based on force and acceleration, according to Newton's second law of motion (F=ma).

Specifically:

One slug is the mass that accelerates at a rate of 1 foot per second squared (1ft/s2) when a net force of one pound-force (1lbf) is exerted on it.

Mathematically:

1slug=1ftlbf⋅s2

In terms of the more commonly used unit of mass, the pound-mass (lbm), one slug is approximately equal to:

1slug≈32.174lbm

This equivalence arises because the acceleration due to standard gravity at the Earth's surface is approximately 32.174ft/s2. Therefore, a mass of 1 slug will experience a gravitational force (its weight) of approximately 32.174lbf.

In summary, a slug is a unit of mass, specifically defined by its relationship to force (pound-force) and acceleration (feet per second squared).

 

[MDriskill]

Many, many thanks to you gents for this technical info - fascinating and a real education. It shows that there is a spectrum of airgun shooting out there!

Frankly, I'm more collector than shooter. "Consistency," "power," and "accuracy" are good enuff if my old toys will run a decent 15-shot chrono string, hit a small reactive targets at 25 +/- yards with iron sights, and give it a good whack. 10-meter matches, field target, sihouette, bench rest, humane hunting, and many other disciplines require going well beyond that, and I very much appreciate your insights.