Understanding cartridge efficiency

[antelopedundee]

I am gobsmacked to see why some members keep trying to deny or "work around" the most basic fact of ballistics. "Regardless of case shape, the same amount of powder, behind the same bullet, in a case of same interior volume will produce the same velocity".

That is fact. Period.

All the rest of his thread is opinions, advocation and use of bandwidth.

So if you take my earlier example of the .284 Win and shorten the case and increase the diameter until it is frisbee shaped and load both cases with the same amount of the same powder will you get the same velocity? Has anyone ever tried this to see if it is true? Taking the .25-06AI and reducing case length until it is equal to the .25-06 will likely give near identical velocities since case design has not changed much. Course the whole idea for the .25-06AI is to get higher velocity at the expense of more powder.

While I don't own one or have the desire to own one it seems to me that the 6.5 Creedmoor is a more efficient cartridge than some larger capacity cartridges. For the most part a 200 fps difference in mv won't have that much effect at ranges at which a lot of deer sized critters are taken.

 

[LVJ76]

The issue is whether a couple of AAA's would keep it going and going as well?

As you can see batteries aren't required Lol, just keeps on going

 

[Stiltsville]

As you can see batteries aren't required Lol, just keeps on going

You're correct. Appears few if any read the Gun Digest article I posted a link to.

More fun to just keep asking the same questions that have already been answered multiple times.

Yes ! "lopedundee" a frisbee shaped 284 would achieve the same ffps as one .284 diameter and 6" long IF they had the same case volume and powder charge !
Hint: a 8 ounce glass holds 8 ounces of water regardless of its shape.

 

[antelopedundee]

You're correct. Appears few if any read the Gun Digest article I posted a link to.

More fun to just keep asking the same questions that have already been answered multiple times.

Yes ! "lopedundee" a frisbee shaped 284 would achieve the same ffps as one .284 diameter and 6" long IF they had the same case volume and powder charge !
Hint: a 8 ounce glass holds 8 ounces of water regardless of its shape.

Of course, but once the powder is burned it then becomes a gas flow issue. I doubt that it's the same for both case shapes.

Also you can pour 8 ounces of water out of a glass way faster than you can pour 8 ounces of water out of a beer bottle. Funny that if you neck a .378 Weatherby down to .17 caliber you can't get 7000 fps out of it.

 

[elkaholic]

Exactly.
You can put enough Red Dot in a PRC to make 65,000 PSI but it wont run 3000' I bet!
You can argue thats not the same, but the fact is its the same situation I argued earlier about the bullet moving up the barrel with different ignition time which changes the curve.Thats why a different shaped/length case acts differently and why the same CHAMBER PRESSURE may not give the same MUZZLE VELOCITY!
If you think about it, its also why +P throating works. It still builds pressure engaging the lands at the same distance but INITIAL PRESSURE is lower. Yes, you then have to increase the charge to get back to the same speed but you can then increase it more and gain even more speed ending up back at the same pressure as the original land configuration, but with more velocity because you changed where the pressure peaked!
It's not exactly the same method used as a shorter burn column, but the same principal at work. The bullet is farther up the barrel before pressure hits its peak. Its also why different powder burn rates change things.
Its not as crazy as some people would like to make it!
Here is an example that Ive used before. My 338 ss and 338 Sherman are close to the same capacity with the long action version having the most. If I tried to run Varget or W760 in the Sherman like we do in the ss, it would blow the primer right out of the case on the Sherman with a 3 grain lower charge!
Both will reach the same velocity providing you use the correct powder, but with much different burn rates.
We could argue about HOW MUCH affect design has, but to say none, i think is rather narrow minded.

 

[Mikecr]

Seems obvious that gasses expand fast enough for any of our cartridges.
The analogous limits in velocity are not due to some gas expansion/flow limit.
That 17-378W would need incredibly slow burning powder to avoid blowing up (military surplus stuff), and then with a 500" barrel, it might just produce 7Kfps. The condition of bullet at departure would be challenging.
But anyway, the limit there is rate of pressure rise-vs-pressure drop held below failure limits.

These call to extremes won't get us anywhere.

 

[Stiltsville]

What you "think" or what you "believe" is immaterial.

When you find a recognized ballistic lab to support your desires, we may listen.

 

[antelopedundee]

Seems obvious that gasses expand fast enough for any of our cartridges.
The analogous limits in velocity are not due to some gas expansion/flow limit.
That 17-378W would need incredibly slow burning powder to avoid blowing up (military surplus stuff), and then with a 500" barrel, it might just produce 7Kfps. The condition of bullet at departure would be challenging.
But anyway, the limit there is rate of pressure rise-vs-pressure drop held below failure limits.

These call to extremes won't get us anywhere.
View attachment 196991

Of course because of the design/shape of the case. A frisbee shaped case isn't very practical to use. If one had a coiled 1mm tube of the same volume it might not. However the OP required only that the 2 cases have equal volumes. OTOH efficiency is not even a consideration for me for what I shoot. Then there are some Scrooge McDuck types who are so cheap they choose the powder that requires the least amount of powder to do the job. I prefer the advice to use a powder which most nearly fills the case.

 

[antelopedundee]

What you "think" or what you "believe" is immaterial.

When you find a recognized ballistic lab to support your desires, we may listen.

I don't care if you or anyone else listens. I'm not trying to change anyone's mind. FWIW I don't give 2 hoots about cartridge efficiency as it relates to velocity.

 

[Lefty7mmstw]

Seems obvious that gasses expand fast enough for any of our cartridges.
The analogous limits in velocity are not due to some gas expansion/flow limit.
That 17-378W would need incredibly slow burning powder to avoid blowing up (military surplus stuff), and then with a 500" barrel, it might just produce 7Kfps. The condition of bullet at departure would be challenging.
But anyway, the limit there is rate of pressure rise-vs-pressure drop held below failure limits.

These call to extremes won't get us anywhere.
View attachment 196991

to make that puppy usable you would probably have to go with liquid propellent... Even my short throated 7rum is having issues with h50bmg. The 870,869, 8700 ball powder variants aren't really any slower and might actually be worse with poor case fill...

 

[antelopedundee]

If a person was to take two cartridges that have the same case capacity, but one is considered more efficient than the other. What are the pro's of the more efficient case?

So if I take a 6.5-06 and a .17-06 both of which could be said to have the same case capacity, which would you consider to be the more efficient? FWIW the two aren't necessarily suitable for the same tasks.

OTOH the 6.5-06 and 6.5/284 have nearly identical case capacities and there is no distinct efficiency advantage of one over the other. There may be other pros/advantages, but those would be mostly personal preference. Ditto for the .25-06 and .25/284. Efficiency for the 06 series likely stops around the 6mm point as everything less than that neck size results in a grossly overbore situation.

 

[Dr. Richard Gray]

Are you referring to efficiency or quality of cartridges? I've never heard of the efficiency issue in cartridges of the same caliber. However; the better quality cartridges tend to perform better. i.e; .340 caliber comparing Star to Weatherby cartridges; which would you choose? For this caliber I will only use Nosler, Norma, or most preferred Weatherby. The latter usually run $0.15 - $0.20 higher per cartridge. I constantly search reloading sites to find them around $2.00 / cartridge.

 

[Elk Hunter 338]

I was looking at what the 338 SS was doing with the 250 grain bullets. From some of what I have read it is getting very close to the Lapua with a lot less powder.

Very Hard Negative ghost rider!!!

 

[Elk Hunter 338]

Just a question from an interested bystander. If a 338 Norma can basically duplicate the ballistics of a 338 Lapua with the same 300 grain Bergers, wouldn't you say that the 338 Norma is more efficient if it uses less powder to achieve it's velocity? Please don't yell at me. I am interested.

High node to high node ... no it wont

and you will get the same input from guys that have actually shot them side by side out of multiple rifles...