Understanding case efficiencies...

Just thinking about case efficiencies, and would like to understand better.
Often see/hear comments about case efficiencies, and if a cartridge is efficient or not.
Can someone please provide a good description of this, and how the two are determined.
I.e.
Is it the most performance per grain of powder? (initial velocity and retained energy at say 300 yards? Find this hard to determine from most reloading anuals as the various bullet weights do not always give the same powders, making an apples to apples comparison more difficult)
Is it related to case capacity? And if so, how?
And exactly when does a case become overbore? Is it relative to caliber size?
And is there a most efficient bullet weight for each caliber that makes it the most efficient cartridge?
(i.e. I recall reading in the late 80's before I bought my first 280 Rem, that the 160/162 gr bullet was the best bullet for the 7mm/284 caliber, so was the bullet weights I chose to handload first)

Gee Gill I'm no Ballistics expert by a far shot but from what I've read it has something to do with case capacity and bore diameter I think and then you have the optimum powder charge for bullet weight now my brain hurts since I have been trying to recall what I have read years ago.
Maybe some one smarter could explain it.

I've always thought of case efficiency as the measure of how much muzzle velocity you can get per grain of powder- basically a measure of how efficiently the cartridge turns potential energy (powder) into kinetic energy (a bullet of some weight at some speed).

It might be easier to describe in term of inefficiency- what most folks refer to as "overbore". Essentially a cartridge that has more powder than can be burned in the bore- most Weatherby cartridges, the RUMs, 7STW, etc. are all fairly overbore and relatively inefficient.
For example-
With H4350 in a 7-08 with 160gr bullet you can get 2583fps from 43.5gr of powder for 59.3 fps per grain.

Same powder in a 7WSM you get 2918 from 59.5gr for 49 fps per grain for the same bullet.

Go to the 7 Weatherby case and you get 2960 with 61.5gr for 48 fps per grain.

With H4350 and 160 grain bullets...the 7-08 gets more kinetic energy per grain of potential energy- more miles per gallon so to speak- than the 7WBY. Each incremental increase in velocity requires more and more powder to achieve. Between the 7WSM and 7WBY you need 2 grains of powder to get a mere 42 fps increase. You exceed max pressure with any more powder in the 7WBY- nothing else will burn in the bore.

This was more of a thing when we didn't have 400 flavors of gunpowder to match case capacity and bore diameters, but in general- short cartridges are more efficient than long cartridges and large cases on small bore tend to be the worst in efficiency since a lot of powder simply gets ejected from the barrel during firing. Now we have such a wide array of powders with such a wide span of burn rates that unless your cartridge is just horribly overbore or really short- you can probably just ignore it.

My idea of efficient is pretty much anything non-magnum based on the .308 case. About as good as it gets.

hodgeman":15nmw6e6 said:

I've always thought of case efficiency as the measure of how much muzzle velocity you can get per grain of powder- basically a measure of how efficiently the cartridge turns potential energy (powder) into kinetic energy (a bullet of some weight at some speed).

It might be easier to describe in term of inefficiency- what most folks refer to as "overbore". Essentially a cartridge that has more powder than can be burned in the bore- most Weatherby cartridges, the RUMs, 7STW, etc. are all fairly overbore and relatively inefficient.
For example-
With H4350 in a 7-08 with 160gr bullet you can get 2583fps from 43.5gr of powder for 59.3 fps per grain.

Same powder in a 7WSM you get 2918 from 59.5gr for 49 fps per grain for the same bullet.

Go to the 7 Weatherby case and you get 2960 with 61.5gr for 48 fps per grain.

With H4350 and 160 grain bullets...the 7-08 gets more kinetic energy per grain of potential energy- more miles per gallon so to speak- than the 7WBY. Each incremental increase in velocity requires more and more powder to achieve. Between the 7WSM and 7WBY you need 2 grains of powder to get a mere 42 fps increase. You exceed max pressure with any more powder in the 7WBY- nothing else will burn in the bore.

This was more of a thing when we didn't have 400 flavors of gunpowder to match case capacity and bore diameters, but in general- short cartridges are more efficient than long cartridges and large cases on small bore tend to be the worst in efficiency since a lot of powder simply gets ejected from the barrel during firing. Now we have such a wide array of powders with such a wide span of burn rates that unless your cartridge is just horribly overbore or really short- you can probably just ignore it.

Click to expand...

Exactly right.

From my understanding efficiency is easies measured in powder weight and projectile weight vs velocity for a set barrel length. The expansion ratio of bore diameter to powder volume controlling efficiency.

For example in a 20” barrel a 308 will be more efficient than a 7mm08 or 260 given a same bullet weight. Look at 130gr bullet for example.

308 3200fps
7mm08 2900 FPS
260. 2676 FPS
All using CFE223 with 24” barrel all with same case capacity for the most part.


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I’m not a huge believer in case efficiency to be honest. The little 308 and 300 Savage are pretty efficient and will do great things but if I’m wanting to deliver heavier hunting Bullets as a decent fast speed I’ll take the Bigger cases. I think once if you’ve got a slow enough powder that continues gaining speed at safe pressures you never really go overbore.

I don’t think shoulder angles, straight sides or any of the other witchcraft change how a cartridge pushes a bullet. It’s just a holder for powder and it doesn’t care or know how steep shoulder angles are. Now, I do believe in how they act and behave in regards to shorter powder columns and similar making them tune and be friendlier but I don’t think it has anything to do with pushing the bullet faster. Adding steeper shoulder angles, near parallel sides and such arrest cases growing and add more room for fuel but I don’t believe a 280 Ackley just whomps a 280 Remington, it has just a touch more capacity and load data is warmer so we wanna believe it’s getting us someplace.

I fool myself on the efficiency deal quite often. I run 175 Partitions or what have you around 3050-3100 from my Mashburn Super. I could literally do the same thing with a 7mm Wby or STW but instead I split the difference with a 300 Win Mag case thinking the bullet cares where the pressure came from. :lol:

I say load em up and shoot them. I probably need more time becoming efficient. Or at least more than my cases :mrgreen:

Thanks Guys...kind of what I was thinking.

Any thoughts on the ideal bullet weight in each caliber?
Do you look at BC and SD, or back to efficiency fps/gr of powder?

Blkram":2diwxiwj said:

Thanks Guys...kind of what I was thinking.

Any thoughts on the ideal bullet weight in each caliber?
Do you look at BC and SD, or back to efficiency fps/gr of powder?

Click to expand...

I think it's something of a combination of all the factors- as the most efficient bullet weight in a given cartridge may lack SD for reliable penetration, or it may be so heavy that you have a steep trajectory and insufficient expansion velocity. Even with the same bore, powders and cases change the ratio and with the variety of powders, especially the new slow burning powders, previously overbore cartridges can be fairly efficient.

It's kind of tricky, as efficiency really doesn't have anything to do with effective. The .270WIN with the 130gr bullet is relatively inefficient and the 300RUM is a nightmare with all but a handful of powders...but both can be very effective.

O'Connor tended to use the phrase "balance"- the sweet spot between bullet weight, powder charge and speed (he favored speed) that yielded good effect on game.

I think your ideal bullet depends upon your intended use/need. If your hunting large dangerous game, you want lots of mass and all the energy you can develop. Fps is not always your best friend, energy and penetration can be far more desirable in hunting situations, but not necessary for punching paper several football fields away. For me efficiency is a sliding scale depending upon intended use.

SJB358":3jzm1lxr said:

I’m not a huge believer in case efficiency to be honest. The little 308 and 300 Savage are pretty efficient and will do great things but if I’m wanting to deliver heavier hunting Bullets as a decent fast speed I’ll take the Bigger cases. I think once if you’ve got a slow enough powder that continues gaining speed at safe pressures you never really go overbore.

I don’t think shoulder angles, straight sides or any of the other witchcraft change how a cartridge pushes a bullet. It’s just a holder for powder and it doesn’t care or know how steep shoulder angles are. Now, I do believe in how they act and behave in regards to shorter powder columns and similar making them tune and be friendlier but I don’t think it has anything to do with pushing the bullet faster. Adding steeper shoulder angles, near parallel sides and such arrest cases growing and add more room for fuel but I don’t believe a 280 Ackley just whomps a 280 Remington, it has just a touch more capacity and load data is warmer so we wanna believe it’s getting us someplace.

I fool myself on the efficiency deal quite often. I run 175 Partitions or what have you around 3050-3100 from my Mashburn Super. I could literally do the same thing with a 7mm Wby or STW but instead I split the difference with a 300 Win Mag case thinking the bullet cares where the pressure came from. :lol:

I say load em up and shoot them. I probably need more time becoming efficient. Or at least more than my cases :mrgreen:

Click to expand...

This.


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Elkman":2ctyhb5e said:

I think your ideal bullet depends upon your intended use/need. If your hunting large dangerous game, you want lots of mass and all the energy you can develop. Fps is not always your best friend, energy and penetration can be far more desirable in hunting situations, but not necessary for punching paper several football fields away. For me efficiency is a sliding scale depending upon intended use.

Click to expand...

Efficiency like efficacy is relative. What is the best all-around cartridge or load is very conditional. Like Bill said, there are so many different factors that go into it.


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I am tending to think along the same lines;

As long as the bullet design and weight yield a good BC, with a reliable SD for good penetration on your intended quarry, at a velocity sufficient enough to expand reliably on an animal at a given range (personally preferred hunting distance) in your own neck of the woods.

I have been looking at the ballistics of the hunting cartridges that I own and shoot, and seeing what those stats look like. It is interesting to see that I use bullets that range in BC from 0.219 to 0.625, and SD in range of 0.233 to 0.293

I know that in Africa on dangerous game, the preferred SD is 0.300, and in north america, reliable penetration is found with a preferred 0.250
And yet, in the field, on-game performance does not always match up to the numbers, as other factors of velocity, bullet expansion characteristics, retained energy, frontal area and big game animal physiology (bone and tissue impacted) and tenacity all play a role in a clean harvest. Some cartridges outperform their paper ballistics.

It is all very interesting and fun to contemplate. But the real judge is the real world experiences, both well executed, and not.
And I agree, finding the balance in one's expectations is important as compared to realistic results.

Hogeman,

You are comparing apples with oranges. Energy goes up with the square of the velocity. If you are going to compare the efficiency of a case based on the energy of the powder burned, then you have to compare it to the bullet energy produced, not the velocity. Short fat cases, for example, produce the same velocity while burning less powder than some longer skinnier cases which means they consume less powder energy to produce the same bullet energy, and thus are more efficient.

Math Teacher":1u8ul47t said:

Hogeman,

You are comparing apples with oranges. Energy goes up with the square of the velocity. If you are going to compare the efficiency of a case based on the energy of the powder burned, then you have to compare it to the bullet energy produced, not the velocity. Short fat cases, for example, produce the same velocity while burning less powder than some longer skinnier cases which means they consume less powder energy to produce the same bullet energy, and thus are more efficient.

Click to expand...

In my example I used the same powder and the same bullet as constants and divided the MV of the load with the amount of powder it took to get there. It doesn't matter that the 7WBY is faster, it used the powder less efficiently to get it there.

Sure, the same 160gr bullet traveling faster does have more kinetic energy, but that's external ballistics...not internal. You could calculate the "foot pounds of energy" at the muzzle/grains of powder, but since the mass is constant the results for efficiency will be the same.

The 7-08 load produces 2370 ft/lbs with 43.5gr....so 54.48 ft/lbs per grain.

The 7WBY load produces 3113 ft/lbs with 61.5gr...so 50.61 ft/lbs per grain....it's still using the powder less efficiently to generate the energy of the bullet in flight....because a bunch of it is burned outside the barrel.

Efficient case- 250 Savage- Mr Newton knew what he was doing. PO Ackley thought so. Is the 22-250 flatter shooting, faster. Of course. but a 100 Gr BT isn't an option, With the savage it is. Its a bit of an extrapolation, but apparently Mr Emery thought so too, everybody is buying a 6.5 creed. More isn't always THE BEST. Now I cant say I UNDERSTAND it all, but those guys do.... Oh David Tubbs set 1000 yard records with a 250 Savage case necked down to 6mm. Sorry I hadn't beat the drum for the lowly 250 Savage in a while.... Forgive me. CL

No worries CL! Appreciate the little Savage too!
My wife and I each have a 250 Savage and I have a 250AI. Would love to have a Savage 99 in 250-3000 so that my daughter can also pack one when we all go hunting together. Have been thinking a BLR TD with a 250 Savage barrel, and a 338 Federal barrel would be very cool too. (and maybe one of those 375 Raptors to round it all out!)

Hodgeman,

Following your line of reasoning, as velocity goes up efficiency goes down. Using the same cartridge and bullet but adding more powder to get more velocity will result in less efficiency. Since the energy of the bullet goes up with the square of the velocity, doubling the velocity quadruples the bullet energy. However since you can't get something for nothing, you have to put in at least four times as much energy in the form of powder burnt to get twice the velocity.

The only way you can compare efficiency by velocity is if two cartridges push the same bullet with the same powder to the same velocity. Then whichever burns the least powder is indeed the more efficient with that bullet and powder at that velocity.

Blkram,

I'm a bit late to the party. Regarding generic case efficiency, I think the usable / working definition varies a lot depending on use. For me as a hunter speed + SD per grain of powder determines efficiency.

As a youngster I purchased a 280 Rem and started reloading rather than purchase a 30-06. I saw that a 175 grain bullet from the 280 Rem had a significantly better sectional density than a 180 grain 30 cal and the 175 grain bullet could be launched about as fast than a 180 grain from a 30-06. Same with 160 vs. 165 grainers.

In competitive shooting I have generally heard the working definition being close to; an efficient cartridge is having as little powder possible to maintain supersonic flight at the desired range. A general primer I would refer to is: https://www.ssusa.org/articles/2016/11/ ... -a-primer/. In competitive shooting, ballistic coefficients, recoil, throat erosion, etc. come into play in defining efficiency. In short range benchrest competitions the lowly 22LR's can rule, while thunder boomers rule past 1000 yards.

For hunters, I generally hear a working definition that deals with energy per grain of powder. For example: http://blog.westernpowders.com/2016/07/ ... fficiency/. The idea being to get as much damage as possible per grain of powder; hunters aren't looking to necessarily shoot at extended ranges with heavy & high BC bullets.

Regarding your comments: "I have been looking at the ballistics of the hunting cartridges that I own and shoot, and seeing what those stats look like. It is interesting to see that I use bullets that range in BC from 0.219 to 0.625, and SD in range of 0.233 to 0.293

I know that in Africa on dangerous game, the preferred SD is 0.300, and in north america, reliable penetration is found with a preferred 0.250

And yet, in the field, on-game performance does not always match up to the numbers, as other factors of velocity, bullet expansion characteristics, retained energy, frontal area and big game animal physiology (bone and tissue impacted) and tenacity all play a role in a clean harvest. Some cartridges outperform their paper ballistics."

I agree 100%.

Thanks Nimrod84.

I have actually been doing a charted comarison of the the cartridges that I own. Something to do on these cold winter evenings! LOL
To try to make it as much as an apples-to-apples comparison between different cartridges of the same caliber (i.e in 0.284; 7mm-08 Rem, 280 Rem, 284 Win and 7mm STW, with AccuBond bullets loaded with Re-19 powder) Sorry, do not own a 7mm Rem Mag at this time. Should put it in for fun.
I used the same bullet and weight and same powder for each to conduct the comparison. Unfortunately Nosler used 24 and 26" barrels for these 4 cartridges, and I used #'s given. I have not extrapolated velocities to make truly equal, say with a 24" barrel. (If I do, I will deduct an avg of 25 fps/inch from the 26" barrel data and run the new velocities in the ballistic calculator again)

For the comparison I included the following data: (100 yard increments to 500 yards with a 200 yard zero; using 500 yards as it is the farthest that I can shoot at our range for practice, and therefore is my personal max for hunting)
Case capacity, weight of bullet, BC, SD, powder charge, load density, fps/grain, ft-lbs/grain, velocity, energy, trajectory, % of retained velocity and % of retained energy.
I did the comparison for all 4 with the 140, 150 and 160 gr AB's. Looking to see if the old 7mm/160gr optimum bullet weight holds up.
Still need to review all of the compiled data to determine which is the most efficient (on paper). Just been gathering data so far.
The other thing I want to do is determine hunting yardage for big game classes, using the old numbers of 1000 ft-lbs for deer, 1500 ft-lbs for moose and 2000 ft-lbs for elk.

Can share findings with people afterwards if interested.

While I have not yet taken game with the 7mm-08 as it is still being built, and the 284 as I hunted with the 338 Federal this fall, and only harvested a caribou; I have taken quite a few animals with the 280 Rem, 7mm Rem Mag and 7mm STW over the past 30 years. These are very effective cartridges, and I like them all. While I like the 280 Rem the best, my favourite hunting rifle is my lh Sako in the 7mm STW. And I have taken more game with it than with any other rifle in my battery.