Basic physics: Why do lighter bullets have exponentially more energy?

Aguila Blanca said:
....What we're not addressing is the INPUT side of the equation: both projectiles are fired from cartridges loaded with the same charge of the same powder. Whatever bullet weight is used and whatever muzzle velocity is produced, it is the result of the SAME AMOUNT of energy created by the ignition of the powder charge. In a closed system, the same amount of energy on the input side should result in the same amount of energy on the output side.

But if one projectile produces more muzzle energy than the other ... something must be getting lost somewhere in the firing cycle. I think the OP is attempting to grasp where the loss(es) occur(s)....
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The problem is that we can not find data that supports the premise that the OP presented in his question, that the same powder charge produces more energy with the lighter bullet. Quickload, GRT and every reloading manual that I have shows that the heavier bullet will produce more energy with the same powder charge, or in other words, a larger powder charge is required for the lighter bullet to produce more energy.

The OP has not provided the details of the powder, charge weight, or bullet type to support his velocity numbers for the two bullet weights. I conclude that there is no mystery here, the two bullet weights perform just like we expect them to behave with the heavier bullet having higher energy than the lighter bullet with the same powder charge.
 
The OP hasn't been back in a couple days, maybe he's just busy, or maybe he figured out what he wanted to know, or perhaps, he's been scared off by the well meant but effusive "technobabble" going into more detail than he was looking for, and I think a bit off into the weeds.

This is his question, as of his most recent postl

My question is really simple:
For the same powder charge (same chemical energy), lighter bullets come out with more KE than heavier bullets.
Clearly, heavier bullets are less efficient in converting the explosion into kinetic energy.
Where is the loss happening?

In particular, what are the losses that are directly related to bullet weight?
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Let's discuss this a bit, and see if we can all get on the same page for what we think he means, and is asking.

First, I think that the example he is using is not about powder charge, and certainly not about what specific powder do in real world cartridges. I think what he is asking about is bullets launched with equal force, and how their energy numbers are different, and why.

IF different weight bullets were launched with a spring (mechanical energy) and that energy were constant, his question would still be the same. So I think focus on the powder charge isn't answering the question.

Next point, one that confuses me a bit, is that while he has said he understands that the difference in KE if the result of the difference in velocity, he feels heavier bullets are less efficient converting the energy driving them into KE and that there is a "loss" that is the cause of this, and he wants to know where that loss is.

Having read the replies, and seeing where this has been explained to him by several different people a few different ways, I'm not sure what he isn't getting.

TO me, in order for there to be a "loss" you have to have had the thing in the first place, in order to lose it. As I see it, heavier bullets with less velocity than light ones haven't lost anything, they never had the speed of the light bullet to begin with.

Thoughts??
 
44 AMP said:
First, I think that the example he is using is not about powder charge, and certainly not about what specific powder do in real world cartridges. I think what he is asking about is bullets launched with equal force, and how their energy numbers are different, and why.

Thoughts??
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In this case. the same powder charge does not produce the same force. If the 185 grain bullet is loaded to the same OAL as the 230 grain bullet, then there is more volume in the cartridge behind the bullet. Less volume results in lower pressure, and less pressure results in lower force.

So while you changed the discussion to equal force, the question the OP raised in his original post was "So, how come the same powder charge is converted to different kinetic energies?"

To get to equal pressure/force, we need to increase the powder charge for the 185 grain bullet compared to the 230 grain bullet. That is supported by data in every reloading manual that I have. There is no mystery here, the premise of a 185 grain bullet having more KE than the 230 grain bullet with the same powder charge with all other factors held constant is inconsistent with actual data. Perhaps the OP assumed that the same powder charge would result in the same pressure, but that is an incorrect assumption. We really need the OP to explain how the velocity numbers in his post were generated.
 
The calculation of KE is the mass times velocity squared. Period. No other values matter. How the bullet got to that velocity does not matter. Whether it was chemical reaction as in gun powder, magnetic rail gun or something threw it at that velocity does not matter.
The amount of energy required by whatever means to get it to that velocity is a separate matter. The relative amounts of energy between the two will depend on the efficiency of the system.

NRA Benefactor
 
In this case. the same powder charge does not produce the same force. If the 185 grain bullet is loaded to the same OAL as the 230 grain bullet, then there is more volume in the cartridge behind the bullet.
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IF. If loaded to the same COL, yes. But not all are. If the bullets are loaded to the same depth in the case, then the powder space will be the same, and the COL will be different.

I think the OP was saying "same powder charge" for both bullets, meaning the same amount of "chemical energy" being applied to both bullets. And, I think the way he worded it is causing us a bit of confusion about what he's actually trying to find out. Both of his posts use terms in ways that lead me to think he doesn't understand some things the way we do.

I suggested considering spring driven bullets as a way to illustrate a constant and equal force, and avoid all the many different factors that can change the pressure of powder charges, in order to focus on what I think the OP was asking about, why "equal force" gave different KE results.

I think all the detailed explanations of powder behavior in the thread have been accurate and correct, but, so far, it seems the OP has not been able to grasp that and we won't know until he posts again.

I think his question is essentially, "if you push them equally, why do you get such different results", and I think he just assumed equal powder charges push them equally and is not aware of the factors that can result in the same powder charge yielding different pressures.

To get to equal pressure/force, we need to increase the powder charge for the 185 grain bullet compared to the 230 grain bullet. That is supported by data in every reloading manual that I have. There is no mystery here, the premise of a 185 grain bullet having more KE than the 230 grain bullet with the same powder charge with all other factors held constant is inconsistent with actual data.
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I disagree. I just don't see things that way, absent more information relating to the specific loads. Here's my viewpoint, and, its going to contain that dreaded word "if". :D

IF the powder space in the case is the same (and it may not be, but IF it is) how can the same amount of powder, in the same amount of space produce different pressure??

COL is not an accurate representation of the amount of powder space. I have a Hornady book showing 2 different 185gr and 2 different 230gr bullets and the COL for each one is different. Hornady might be seating these bullets so the depth of the bullet base in the case is the same (which would make the available powder space the same) but there is no information given saying that is what they do. I guess it is implied, but not stated??

Loading different length bullets to the same COL, obviously means the bases are at different positions inside the case, and so the powder space will be different. SO, as I see it, COL can give you an indication, but not an actual amount without additional information.

Also, with all other factors held constant, won't the lighter bullet have higher velocity, and therefore the formula will result in a higher KE number due to the difference in mass not being as much of a factor in the formula as the difference in velocity, squared?

Perhaps the OP assumed that the same powder charge would result in the same pressure, but that is an incorrect assumption. We really need the OP to explain how the velocity numbers in his post were generated.
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this, I can absolutely agree with.
 
The following may or may not be relevant.

I recently had a question (legal, not firearms related) that 'no one could answer' (in my later life I think I should trademark that phrase).

Knowledgeable folk tried to answer my question but they just didn't REALLY understand what I was asking. Everything was polite and there were no real hard feelings, but I wasn't satisfied.

Then a couple of days later, while I was working on some fiddly workbench stuff I realized what the knowledgeable folk had been trying to tell me and how it really did answer my question.

Long story short, I had a blind spot that prevented me from understanding. I don't know why it was there and I don't know why it went away but it left me feeling awfully sheepish.
 
44 AMP said:
.... I disagree. I just don't see things that way, absent more information relating to the specific loads. Here's my viewpoint, and, its going to contain that dreaded word "if". :D

IF the powder space in the case is the same (and it may not be, but IF it is) how can the same amount of powder, in the same amount of space produce different pressure??

COL is not an accurate representation of the amount of powder space. I have a Hornady book showing 2 different 185gr and 2 different 230gr bullets and the COL for each one is different. Hornady might be seating these bullets so the depth of the bullet base in the case is the same (which would make the available powder space the same) but there is no information given saying that is what they do. I guess it is implied, but not stated?? ....
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Let's look at the data in the Hornady manual, mine is the 9th edition. There are four powders in common for the 185 grain bullet at 1000 fps and the 230 grain bullet at 850 fps. Here are the powder charges for the 185 gr @ 1000 fps vs the 230 gr @ 850 fps:

Power Pistol: 8.2 gr vs 6.7 gr
Longshot: 8.7 gr vs 7.1 gr
4756: 8.8 gr vs 7.3 gr
HS-6: 10.1 gr vs 8.2 gr

That's a significant difference (over 20%) in powder charges between the 185 gr and the 230 gr. Unfortunately Hornady does not list pressures, so I used Quickload for a few predictions for XTP bullets and Power Pistol powder.

Quickload agreed closely with the Hornady velocity data; Quickload predicted the 230 gr at 16.8k psi max and the 185 at 17.4k psi max, reasonably close. The useable case volume was not equal, the 230 XTP at COL of 1.21" had 12 gr water vs the 185 XTP at COL 1.213" with 14 gr water.

Adjusting the COL for the 185 gr bullet to get the same useable powder volume (1.156" vs 1.213") and using the same 6.7 gr powder charge as the 230 gr, the predicted pressure is 14.3k psi, 2.5k psi less than the 230 gr. The 185 gr bullet is easier to move down the bore so less max pressure at the same powder charge and useable case volume. EDIT: To get to 17k psi max at this COL in Quickload, the powder charge was increased from 6.7 gr to 7.3 gr.

Adjusting the COL even lower to get the same max pressure (1.12" vs 1.213") gave a predicted pressure of 16.8k psi, but with a COL that may not feed reliably.

So I stand by my statement that all else being equal (COL in the same range, as it is in the Hornady manual), the 185 gr will require a larger powder charge to get to the same max pressure as the 230 gr.
 
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44 AMP said:
First, I think that the example he is using is not about powder charge, and certainly not about what specific powder do in real world cartridges. I think what he is asking about is bullets launched with equal force, and how their energy numbers are different, and why.

IF different weight bullets were launched with a spring (mechanical energy) and that energy were constant, his question would still be the same. So I think focus on the powder charge isn't answering the question.
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Well, he specifically said the same powder charge, but you may have a point about that not being possible. Your comment reminded me of an article I read on the Shooting Times web site several years ago. I copied it and saved it for the simple reason that the examples were based on .45 ACP (which is what I shoot, Winchester 231 (which is what I use for most of my handgun reloading), and two of the three bullets discussed (Berry's 230-gr round-nose and Berry's 185-gr hollow-base round-nose) are what I load.

Here's the article: https://www.shootingtimes.com/editorial/power-factor-recoil-bullet-weight-gives-edge/99399

For some reason, the images aren't showing up for me now, so I have to refer to the copy I made to see that charts and tables. What the article is about is making a 165 power factor with different bullet weights.

What the author found was that with a 230-gr bullet to make 165 power factor he needed 5.2 grains of powder, but to make the same power factor with the 185-gr bullet he needed 6.6 grains.

Viewed another way, he also included a chart showing the resulting velocities and power factors for representative powder charges. What that table shows is that FOR THE SAME POWDER CHARGE lighter bullets do NOT achieve higher velocities -- they are slower.

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This supports my own findings that I typically needed more powder to drive a lighter bullet to the same velocity (not muzzle energy) as a heavier bullet.
 

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Sorry for not posting again.
I am definitely still interested in this.

Thing is, actually... :)
Last time I loaded my own was 10 years ago. I can't even remember the brands of components used. I only remember I used the same amount of powder.

At the time, I didn't care. I "knew" lighter bullets come out faster and get more muzzle energy.
Same way I knew a 3GHz processor is faster than a 2GHz processor - I didn't stop to think "why" until I studied electronics engineering.

I'll read carefully all the comments over the weekend.

I can't replicate and demonstrate the problem with a firearm, as I currently live abroad.

How about a spring air gun?
The piston is very consistently loaded to the same energy state.
And it has the added benefit that airgun pellets have very similar friction profile, no matter their weight - they all seal at the skirt, which gets blown up by the pressure and expands to the diameter of the barrel - but the contact area must be pretty much the same (very small) - so, it's only going to be the weight that significantly changes...
Sunday I'll have access to a chronograph at the local range :)
 
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Just skimming the answers I see I could have totally got it wrong and lived in a lie for decades :D

Now I am not 100% sure the sun will rise tomorrow ;)

I guess while the discussion wasn't progressing humanity and helping everyone involved transcend to a space fairing civilization, it did fix a misconception I had and it made a difference to ONE person :)

Thanks for all your lovingly prepared answers :)
 
Yes, the OP did say "the same powder charge" and he also said "same amount of chemical energy, and he also said this,

A) I load a 45acp with a 230-grain bullet and it does 850fps = 370 ft-lb of energy
B) I load the same shell with the SAME powder charge with a 185-grain and it does 1000fps = 411 ft-lb of energy
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Not mentioning anything about what powder or charge was involved in creating that data.

It may be we are chasing our tails, arguing about how many angels can dance on a pin trying to explain what may be the OP's flawed understanding, or perhaps just use of terms in a way I'm sure he understands but leave doubts in the rest of us.

As for the data in a Hornady manual, I'm sure they accurately report the results they got with what they tested. One manual gives one set of data and another gives another, and slightly different set of data. I've got manuals that list powder charges a couple tenths off (Both higher and lower) than yours does.

Your gun is not their test gun. My gun is not their test gun, and it won't be the OP's gun, if he has one, and absolutely identical results across the board I would put down to serendipty or simply random chance. The manuals are guidelines, not holy writ and while one expects similar data no manual should be considered unalterable dogma.

Also, considering that Hornady lists the velocity in blocks of 50fps, one cannot and should not expect too much precision. And, its not needed.
 
I’ll take a light fast bullets over heavy ones for any given rifle caliber/cartridge if available; this is for anything intended for mammals and/or large aggressive reptiles or fish that may have come on land to challenge me lol. Don’t really care when it’s plinking.

Just my opinion based on my own experience, higher velocity bullets work better for me.
 
The easy answer is energy transfer. The lighter bullet has less inertia, therefore it is able to receive more energy from the powder in the short amount of before it leaves the barrel.

The downside is that the lighter bullet also loses energy quicker because of the lower inertia. This is why long range hunters/shooters prefer a heavier bullet, which retains energy better at longer range by losing less energy to drag. Obviously ballistic coefficient plays in, but the principle is true even without factoring in BC.

This is not complicated.
 
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