Understanding cartridge efficiency

Stiltsville

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This thread is amusing to say the least.
Wild claims of case shape affecting efficiency with no lab backup.
The Handloader test being dumped on when it was the only one with lab support.

If anyone wishes to make odd shaped cartridges that they believe are better, have at it.

Hate to tell you how many bets I have won with my 300 H&Hs from fellows who thought their 300 WSMs were more efficient hence faster.

I won't even get into reliable feeding -------
 

JASmith

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To determine relative efficiency, one can look at the kinetic energy for two different cartridges with the same bullet and powder. The charge weights can be be different because we will compare energy as a fraction of available energy of combustion in the powder.

The one with the greater energy per grain of powder will be the most efficient.

This tends to favor smaller cases and longer barrels.
 

epoletna

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Stiltsville uses the example I was going to bring up: the .300 H&H versus the .300 WSM. Two extremes in case design, and you can see from ballistics tables how they stack up.

This reminds me of a comment I made in this forum in the past two years: three classic cartridges from the last century are remarkably alike in profile: the .50 BMG, the .30-06 and the .223. It is not a perfect duplication from one to the other, as the .223 is a little "stubbier" than the other two, but there is no extremely different case profile.

Then as we reach the last half of the last century we begin to see a movement toward shorter and fatter cases, mostly with a sharper shoulder: the 6 PPC and the various Creedmoor variations.

Either powders began to burn with different pressure curves, or wildcatters began to notice that shorter cases with greater diameter used the powder better. Does "better" mean more efficiently? I don't know the answer to that, except to note that the "newer" designs seem to use less powder than the older case designs to achieve the same velocities. I suspect the shorter/fatter designs recognized the difference between burning black powder (older, straight-walled or long-taper cases) and burning smokeless powders (shorter/stubbier cases, but with sharp shoulders). All of which raises the question "should we try new designs even shorter and fatter"? Magazines and action ring diameters probably make that impossible, but if you could get around those limitations, would shorter and fatter improve efficiency?

Ackley was chasing this equation half a century ago. And we're still chasing it. I like to think we're getting more "efficiency" out of our cartridges and powders, but I cannot make that argument with more than anecdotal evidence.
 

bigngreen

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We all are looking for different things down to how a case even looks sometimes, some like to shoot small, some like to launch missiles some just like volume shooting, to get our panties wadded up over this stuff is kinda like burning you own house down because something made you mad!!

There are things we can manipulate in case design, when we chamber and finish and how we load separating out those things is difficult at best, one thing I can't control without major over haul is the case heads response to pressure, there is some ways to work with it in some smaller cartridges but it's much harder the bigger we go.

When I make everything the same, not talking radically different but as exact as I can down to surface finishes, base diameter on the reamers, throating, brass, matching everything I possibly can BUT have different shape and I see 100+ fps difference at the same case head measurements how would YOU interpret that? The only thing I can do is think there is something in design that changes how the powder lights and burns.

There are guys who are shooting sub inch groups at 1000 yards more and more regular, 2 inchers are common they did not reach that point by managing large things but it's in the minutia that many just don't believe or care is there. These guys are applying what they know to farther ranges and learning a whole other set of lessons and for some the continual learning process is the fun part, it's interesting to watch!!
 
Last edited:

thwatson2

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Nov 4, 2012
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The efficiency is more about the same caliber performance. 30-06 and 308 are gonna throw a 165 grain bullet within 100 FPS of each other. Cartridge capacity of 56 grains vs 68 grains of powder. Therefore for very little performance the 308 uses less powder in a shorter cartridge. It technically has a shorter burn column and should chamber easier within a shorter action. Therefore we consider the 308 more efficient
 

huntintoo

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If I was only looking for efficiency, I wouldn't be favoring my .300 Weatherby Mag. But accuracy and reach are also in my factors.
.338 Edge is also not easy on the powder. But I hold her dear to my shoulder!😍
 

Weatherby Fan

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Maple Ridge, BC, Canada
There is no such thing as cartridge "efficiency" as Handloader proved several years ago with their 300 WSM vs 300 H&H test.

Roy tried to peddle this BS in the 1950s and people fell for it. They still do.
So many variables to go along with “cartridge efficiency” from primer used to powder, barrel length, just the tightness of the barrel bore, throw in a little neck tension can even change things up.
My brother and I have the exact same rifles and cartridge and his shoots 80 FPS faster than mine on average with the same handloads or factory ammo, we even used the same box of factory ammo and had the same result, only mentioned this as to show variables in two of the same rifles and cartridge never mind two different cartridges with similar case capacity.

with that being said for example I would take the 300 PRC over the 300 Win Mag everytime just based on cartridge design, no belt, steeper shoulder angle, longer neck etc, is it more efficient in that design ? that’s for someone way smarter than me to figure out !
 

Stgraves260

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Sep 1, 2009
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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?
The closest thang I can figure out what your talking about would be something like this. Let’s compare a 7 Rem Mag and a 7WSM. The 7 RM holds 83.2 H2O and the 7 WSM hold 83 H2O. So if Winchester’s claims are correct and they can get the same FPS out of the WSM as the 7 RM with grain per grain bullet weight that would be 1% more efficient. You get the advantage of a shorter rifle. The 7 Mag would need a 26” barrel to achieve the same ballistics as the 7WSM with a 24” barrel. I thank that’s what your talking about. Hope this helps.
 

Snowboy

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Ontario Canada
Long winded, and forgive me if you already know this.
As a reloader, cartridge efficacy is what gives me the best brass life, minimal maintenance, and outstanding performance. Some of the things that enable that are 35° or 40° shoulders, long enough necks for good bullet seating and minimal runout, slight taper for easier extraction without increasing rearward force on the bolt face, excellent magazine fit and feed capability, etc. These are many of the things that P.O. Ackley did in his case modification experiments.
An internal ballistician can tell you about efficiency. Borrowing a page from the Manhattan Project, if you really wanted to maximize the efficiency of your cartridge, you would "shape" the powder charge and load the cartridge with layers of powders of different burn rates and charge densities, focusing the shock wave. Problem is, you'd probably pulverize the bullet before it even left the chamber. Bullets are cheap. Quantity thereof and the quality of their use tends to win.

Seems to me, in your thirst for efficiency knowledge, you are asking about same powder charge, same bullet, different velocities. You may well know, the only way to test this would be same barrel/powder/bullet etc. I read posts here and on other forums where people are loading cartridges like 338 LM with the same powder, charge, bullet weight, primer and brass that I use, in a barrel 2" longer, and they're getting 200 FPS more muzzle velocity than I do. I scratch my head and wonder, WTH am I doing wrong? Mind you, their rig might be a Defiance action with Krieger or Shilen barrel, same twist and mine is a Savage 110BA. So, no matter what the cartridge might be capable of, YMMV.
All that said, I offer this comparison of 7mm Cartridges, the first two with similar case capacities, for your review:

View attachment 196530
Just to add more confusion ask yourself which cartridge is easier for you to shoot accurately. (How hard does it kick)
 

ofbandg

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Jul 26, 2015
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Efficiency is finding the best way to achieve your goal - and we all have different goals. I have always looked at efficiency in a hunting rifle as something that gets the job done with the least amount of effort. For example, you can load a .270 Win. with a 180 grain bullet, a 30-06 with a 180 grain bullet, and a 338-06 with a 180 grain bullet and they will use approximately the same amount of powder and produce the same amount of recoil, but the 338 will give you superior velocities. Others might prefer the 30-06 because it has a better BC for longer range. It depends on your goals.
 

Buckys

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Nov 13, 2018
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Tejas
I would be interested to read this if someone knows where to find it:
There is no such thing as cartridge "efficiency" as Handloader proved several years ago with their 300 WSM vs 300 H&H test.
 

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