Cartridge efficiency

[lkramer]

Ran across data for 6mm30AR: 105gr bullets @ 2900 fps (from rebarrelled Rem AR30) Source: Westex at 6mmbr.com forum

BillK (benchrest.com forum) posted that his 6.5 WSSM uses 8.5% less powder (48.8 gr. RE22) to shoot 140 gr. bullets @ 3070 fps than his 6.5-284 uses to shoot the same 140 gr. bullets @ 3070 fps.

Also found 6BR AR uppers and magazines (tested in Natl. competetion) are also available at BR Armament (bratrifles.com)

 

[willypete]

Yes, some cartridges do the same job as others with less powder burnt or at a lower pressure.

Good luck finding those cartridges at WalMart/LGS/etc.

Are you trying to highlight some cartridges, start a debate, what?

 

[klmspider]

cartridge efficiency note

When I surveyed most loads, just browsing data, I noticed that the military loads usually gave the better performance of energy for amount of powder burned, among most other rounds.
I'm referring to specific shell casings that a military use versus a cartridge specifically designed for the commercial sportsman market.

 

[Owen Sparks]

Compair loads with 150 to 168 grain bullets in the .30-06 with the .308 to get a good idea of how much more efficent the shortened case can be.

 

[MachIVshooter]

Smaller cartridges, like small engines, are more efficient. But, also like smaller engines, they do not have the same performance potential.

 

[suemarkp]

Efficiency is driven by 2 things -- pressure and case capacity. Put a 110gr bullet in a 30 carbine case and 300 WinMag using the same amount and type of powder. The 30 carbine will go faster because it has less capacity. But the 30 Carbine maxes out with pressure and powder capacity well before the 300WM, so the 300WM will shoot a given bullet much faster when using enough power to max pressure and capacity.

 

[Owen Sparks]

The .30-06 will drive a standard weight bullet a little faster than the .308 but does so at the expence of a good bit more powder, noise and blast as well as a longer, heavier action needed to contain the longer cases. As I understand it, modern .308 military loads are virtually identical in preformance to the WWII version of the .30-06 due to improvements in powder. Some modern .308 loads like the light magnums from Hornady actually exceed the .30-06 loads of yesteryear. The real advantage the modern .30-06 offers is with heavy 200-220 grain bullets because they just take up too much of the limited case capacity to be practical in the .308.

 

[T.R.]

I read somewhere that 35 Whelen is most efficient cartridge case of them all.

TR

 

[KansasPaul]

The article regarding cartridge efficiency that T.R. mentioned was published by Guns & Ammo about 5 or 6 years ago. In that article they used bullet weight, muzzle velocity, powder weight and "lethality". I wish I had kept a copy of the article because it was a good read. However I think I remember a statement in the article that they were not measuring the ballistic efficiency of the cartridge but a combination of several factors.

 

[Kernel]

In the study of Internal Ballistics there is a concept known as Relative Capacity. The inverse is called the Expansion Ratio (ER=1/RC). If you study Internal Ballistics you see these concepts a lot.

They are simply dimensionless terms that describe the ratio of case capacity to bore volume. They’re just numbers, but they can be used as a mathematical shortcut to describe a particular cartridge’s potential efficiency.

In my view, formulas like Relative Capacity/Expansion Ratio are useful since they are devoid of personal bias, options, and antidotal observations.

There’s a link below, at the bottom of that page is a table with the RC of various cartridges with and without a bullet seated in the case (with a bullet seated, case capacity is reduce, effecting the RC calculation). It also describes how you can calculate RC. Piece of cake if you’re good with spreadsheets.

BTW, the .35 Whelen is about in the middle of the pack, making it an efficient cartridge (in the terms of RC/ER - not too high, not to low).

http://kwk.us/powders.html

 

[lkramer]

GET MOST VELOCITY & ACCURACY W/ BOTTLENECK CARTRIDGES (ALL ELSE BEING EQUAL) FROM MORE EFFICIENT/CONSISTENT COMBUSTION YIELDING MORE CONSISTENT VELOCITY (ES) ?
Found this paragraph below (Aspect ratio & consistency) @ Wikipedia: "Internal Ballistics"

Aspect ratio and consistency

"When selecting a rifle cartridge for maximum accuracy, a short, fat cartridge with very little case taper will generally yield higher efficiency and more consistent velocity than a long, thin cartridge with a lot of case taper (part of the reason for a bottle-necked design).[9] Given current trends towards shorter and fatter cases, such as the new Winchester Super Short Magnum cartridges, it appears the ideal might be a case approaching spherical inside.[10][dead link] Target and varmint hunting rounds require the greatest accuracy, so their cases tend to be short, fat, and nearly untapered with sharp shoulders on the case. Short, fat cases also allow short-action weapons to be made lighter and stronger for the same level of performance. The trade-off for this performance is fat rounds which take up more space in a magazine, sharp shoulders that do not feed as easily out of a magazine, and less reliable extraction of the spent round. For these reasons, when reliable feeding is more important than accuracy, such as with military rifles, longer cases with shallower shoulder angles are favored. There has been a long-term trend however, even among military weapons, towards shorter, fatter cases. The current 7.62 x 51 mm NATO case replacing the longer .30-06 Springfield is a good example, as is the new 6.5 Grendel cartridge designed to increase the performance of the AR-15 family of rifles and carbines."

 

[Certaindeaf]

.22 LR is pretty efficient. A five gallon pail of that would put down a heap of meat.

 

[Slamfire]

Gunwriters have to make razor thin differences wider than the Grand Canyon, or else they would little to write about.

Cartridge efficiency is one contrived issue that Ken Warner made a career and he loved to compare and contrast. He called some cartridges "overbore", etc. All sound and fury signifying nothing.

If you want “efficiency” then you want high pressures. The higher the pressure the more complete the combustion. Sounds great?

Not great. High pressures will cause cartridges to stick. The great British African cartridges were highly inefficient. Burnt lots of powder, at low pressures, moderate velocities. But guess what, in the hot African Savannah with large toothy things out to get you, you don’t want a jam because you can’t extract your sticking cartridge.

If you want to push a bullet at X fps and your greatest concern in life is to get 127 rounds from a pound of powder instead of 100, raising pressures will get you there.