Explanation for why heavier bullets get lighter charges

Reading is the first step

When I started there was no help anywhere, you were on your own, Jack O'Connor & Outdoor life magazine and Elmer Keith were about all we had plus our manuals. My first book was a Hodgdon's Reloaders "Catalogue" #6 "this is how Hodgdon spelled catalog on the front of their reloading manual". This was my introduction to loading ammunition, there were few sources of information available at that time but I can say I never damaged a firearm nor had a case separation nor blow or pierced a primer.
When I suggest reading which I do often it is the first step in acquiring the basics so one at least has an idea how they should go about ensuring they do not damage their firearm nor injure themselves or other shooters.. Non the less this hobby forces you to learn a new vocabulary to understand the terminology used by people who load ammunition plus enable other people to learn a new skill. It will take time, eventually you may or may not get there, it depends how badly you want it.. William
 
I'll see if I can add to the confusion.
First,and quite important.Black powder and smokeless powder operate by a completely different set of rules.
I suggest Mike Venturino's book "Shooting the Buffalo Rifle" or something like that.I don't remember the exact title.Also,SPG Bullet lube has a great little handbook for Black Powder cartridge shooting.
I won't tell you you cannot use smokeless in your Sharps.You can
I will tell you Black Powder is a perfectly good choice.Read Venturino.
What you need to know and remember,with black powder,NO Air Space in the case.The cartridge must be filled.Lightly compressed is best.Some space may be taken up with wads or grease cookies.
Another author with good info is Paul Matthews.NO AIR SPACE in the cartridge when using BLACK POWDER.

Now,on to smokeless.

The first caveat to go along with your question,your general rule applies to one specific powder.
What do I mean?Powder comes in different burning rates.

If we choose fictional powder XS 1234 and load a max of 25 gr behind a 300 grain 40 cal bullet,Yes,you are right,you might load a max of 18 gr behind a 400 grain bullet.
Same powder.Heavier bullet,lighter charge.

But often,with a lighter bullet,a different burn rate of powder is a good idea.It will be a better match.Lighter bullets typically work better with quicker powders.Here is the important part,when you change powders,its a whole new ball game.The charge weights are not related.

Example,in a handgun case..these are fictional numbers,I'm making them up,don't use them to load with.

It might be in a 44 Magnum pistol you could load 5 or 7 grains of Boomflash,a fictional very fast,target powder for a mild max load behind a 240 grain bullet,yet with H-110,a slower burning ,maximum performance powder you might load a max of 23 grains or so.(Don't trust my numbers)

I appreciate your quest for a general understanding of the "rules"
I suggest you not try to apply the "rules" to interpolate or assume.
There are a lot of variables.

I suggest:
Read Venturino

Realize the 45-70 is loaded with smokeless to at least 3 different pressure levels.
Level one is Trapdoor Springfield.Old rifles that are not so strong.Your Sharps may be here.MAYBE,depending on the Sharps,you can push this up a little toward the level two,(Is it an old original?A modern replica?What does the maker say? What is it proofed to shoot?)
Next is 1886 Winchester.These are stronger and can take a little more.
But I'd still go easy on 125 year old steel.And your Sharps.

Another partial step up is the modern 1895 Marlin.Modern steel,strong rifle.
Beyond these,is the Ruger #1 and Siamese Mauser Conversions,etc.
These can be loaded to approach the lower end of .458 Win power.
Obviously,not good for your Sharps.

There are developed,tested loads available for each level.

Its good to understand the theories,but for now,I suggest use tested,published recommended loads.
Another useful reference is Hogdon's Reloading Annual.It comes in a magazine format for a reasonable price.
 
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This is absolute bunk.
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Undoubtedly you are with the PC police (Politically correct police). So lets substitute P as pressure instead of F = force, and E as energy the amount of powder needed in the equation. P = M*E the results are the same. Or maybe we should use E=MC2 but I am sure the speed of light does not have that much effect on the amount of gun powder needed, then again it might since these posts are being sent at that speed (or close to it depending on wire resistance.)

If you have a better way of explaining the need for reduced loads for heavier bullets, I would be happy to hear it instead of your snide comments.

Thank you in advance for your explanation and answer.

Stay safe.
Jim
 
Undoubtedly you are with the PC police (Politically correct police). So lets substitute P as pressure instead of F = force, and E as energy the amount of powder needed in the equation. P = M*E the results are the same. Or maybe we should use E=MC2 but I am sure the speed of light does not have that much effect on the amount of gun powder needed, then again it might since these posts are being sent at that speed (or close to it depending on wire resistance.)
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No,I am with the anti ignorance watch group.
And you must be with the bad guys on the other side.
Again,P pressure = F/a that is force on the area it is applied so the formula you
posted is not even real,but it does produce the same results as the other one you gave,garbage.

If you have a better way of explaining the need for reduced loads for heavier bullets, I would be happy to hear it instead of your snide comments.
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Read post #6
 
Let's all take a breath. We're after the same thing. All of us go home with the same number of holes as when we got to the range (i.e., no injuries).

First, thanks everyone for the responses. I'm a firm believer in the idea that there's no such thing as too much safety training, or in this case, safety reading.

Second, I have reread the Lyman 49th. Turns out it does not actually mention a specific answer to my question - at least not that I could find. While I'll buy another manual, I gotta say that no writer can anticipate every question. So I feel comfortable having asked here for follow-up. You all don't know me personally, so it's fair to be skeptical and careful, but I've got no interest in going outside the info in the manual. But I still want to know why the patterns if see in the manual exist. I think that's a fair part of becoming a knowledgeable reloader. Hence my question.

My Sharps is a recent manufacture Pedersoli, but I'll be looking to keep all loads in the neighborhood of Trapdoor/original BP pressures and velocity. I know BP loads can't have any space between powder and bullet.
 
Studying a number of reloading sources, one will find that bullet weight, jacket thickness, bullet length/bearing area, bullet hardness, jacket material, bullet seating depth, and at least a few other things affect the pressure generated in accelerating a bullet to a given velocity from a given case fired in a particular gun. So it's just not one characteristic, but several. And it's not just as simple as F=MA or some simple substitution of different parameters for the real ones. F=MA ignores friction, and the friction of bullets fired in cartridges are a significant variable that greatly affects the final result (pressure).

In general (but not always) a heavier bullet will take up more space in the case and will have more bearing surface. Since that adds up to more pressure, that means less of a given powder will be required to stay below a given pressure level (in general, but not in every case).

Speer's Number 12 loading manual has some very detailed information on the subject. Not sure if the latest edition has as much detail or not.
 
A significant difference between BP and smokeless is that BP is an explosive, smokeless is a propellant. The difference is in burning rates, pressure rise curve and response to pressure. BP explodes regardless of location. The case needs to be full to make sure that you have one controlled explosion rather than a series of them. Smokeless can be less sensitive to volume due to the variety of burning rates, bulk and composition. Can is the operative word because too little of a dense ball powder can result in erratic performance in a large case while a bulky powder will overfill a small case. The manuals are definitely your friend. Information will change with the changes of formulation. Old manuals should be used with old powders.
 
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The OP did read Lyman's 49th. It was in doing so the OP noticed the trend that led to the question we're discussing.

Whilst I too recommend reading that or another reputable manual, I see nothing wrong in asking.

For example, I found info on crimp less than satisfactory in manuals and sought clarity on here.
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I am with James on this one. Good to ask, I am not sure how to interpret the one comment about knowing even if you don't understand.

I am never quite sure how learned we are supposed to be before we ask a questions .

Do we need to be a 10 on a 1-10 scale and therefore don't need to ask questions?

I thought the OP was quite generous in his reply.

I also think we should not get on too high a horse
 
I thought the OP was quite generous in his reply.
I also think we should not get on too high a horse
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I agree. Some folks need to understand the "why" at a deeper level - it's just the way some minds work. And sometimes hearing or reading the same material phrased differently helps it to click. That is part of the purpose of these forums, in my opinion, and I appreciate both questions and answers equally; I am 59 years old and am learning new stuff all the time. Throw the dirt over me when I stop learning.
 
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