Understanding cartridge efficiency

[Lefty7mmstw]

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?

if I were to take your question literally you would actually be asking how big of a hole in the end of the barrel do I need to make my pipsqueak little case make more energy... I run a 270, a 30-06 and a whelen... All burn around 55 grains of single base powder (IMR single base powder all has the same energy per grain content; the difference is in grain size and coating) I do prefer double base in the whelen (rl15) but it eats single base just fine too so the comparison holds
my 270 (130 grain pill-3050 fps) develops 2686 ft# of muzzle energy
my 30-06 (165 grain pill-2850 fps) develops 2976 ft# of muzzle energy
my 35 Whelen (220 grain pill-2700 fps) develops 3562 ft# of muzzle energy

 

[FEENIX]

One of my favorite wildcatter here is @Swamplord, he's got some bad arse wildcats and names to go along with them.

 

[bigngreen]

I think it's a hard thing to look at simply because we have a very limited window into the dynamics of what's going on so we are left with some data points to interpret along with a lot of thoughts along the way.
I've ran very similar case capacities in long and shot powder columns and you can feel a recoil impulse difference, what make that happen, it really has to be how the powder lights and expands with all else as close as we can make it.
Does that equate to effeciency, not entirely certain but there is differences. It could be a mixture of both a small change that puts the load density spot on and we see a better quality ignition and burn rate along with the design encouraging a full burn at a different timing.
It's amazing to me how some little things we do will put you into an entire other burn rate powder and then other things we change seems to be blowing a whole lot of powder for little gain. If the loader uses the same pressure signs like case head expansion or a pressure reading you should expect predictable results but often there are surprises.

 

[degreen]

My original thought behind this was, is how does cartridge dimensions effect efficiency? Given the same case capacity, same bullet weight and caliber. How does the case dimension effect bullet velocity and accuracy if any?

 

[elkaholic]

There are a lot of things that happen in a millisecond of ignition that are difficult, if not impossible to measure. You could have 2 different chambers with identical volume and the same bore, bullet, etc that are both running at 60,000 PSI, but does that mean everything is equal. I dont think so, and heres why. There is no way that a case 3" long with a given diameter and volume will have the same ignition time as a case 2" long with a larger diameter and same volume. That should be indisputable, since the travel time to ignite the column is longer duration, whatever the difference is! Add to that a different shoulder angle which has to cause a different flow of gases. At some point in the process, the bullet starts to move forward. Obviously if the bullet starts moving forward a little earlier because of the amount of powder ignited, you already have a difference in peak pressure time and also how far down the barrel the bullet is when this occurs. I think this has a lot to do with why we SEE differences but cant necessarily measure them with available equipment.
Add to that how well a case handles pressure, and design matters. With low body taper, you have yet another variable which allows more velocity without hammering brass.
I dont see how any logical person could not see this?
Since we don't know exactly what happens, we cant say that there is an exact formula but we can measure results on the chrongraph, we can measure barrel life and accuracy, and we can utilize what we see works for us.
For good reason, we dont see many people developing longer, skinnier cases with shallow shoulders and short necks.
This also makes sense as to why powders act differently in different shaped cases.

 

[Mikecr]

My original thought behind this was, is how does cartridge dimensions effect efficiency? Given the same case capacity, same bullet weight and caliber. How does the case dimension effect bullet velocity and accuracy if any?

I'll try my hand at it, with an example.
An attribute of an efficient system is full powder burn AND a low muzzle pressure. With that, higher % of powder energy is actually used to push bullets. It's an easier path to this with underbore cartridges, but it can be done with smaller hunting capacity cartridges.
Efficient cartridges I know of are 6PPC, 30BR, and 26WSSM IMP. I believe an improved version of 25x47 could add to that small group.

IMO, efficiency itself is not an overwhelming advantage to practical use. Just a side effect of the right powders available for the right capacities and right bullets.
A 26WSSM Imp, having same capacity as a 260AI, can leave any 6.5x284 (which is way larger) back in a ditch throwing up all over itself. Not so much because it's more efficient(even though it is), but because it's the better capacity for best in cal bullets.

 

[highdrum]

Efficiency is usually the claim by wildcatters used to replace the phrase overpressue. If you have to use srp brass in ur creed or 308 based case to keep primers more than 2-3 firings, you're over pressure, not efficient.

If you're manipulating case geometry to what is basically a square walked cartridge with a 40° shoulder and running high velocities than cases with 10%+ more capacity, you're not being efficient, you're loading over pressure.

We also need to establish what's over pressure? It's a personal choice I guess. You can call it efficient, I'll obviously call it another matter. Yes I've ruined brass by loading too hot in just a few firings, adg and lapua no less. I've stuck a case in the chamber that had go be driven out with a cleaning rod, it was a sherman max. I've pushed the envelope and learned a lot of things. If something sounds too good to be true, it probably is. Corners are getting cut or someone's cheating. If you want a bullet to go fast, it takes one thing, and that's the size of a case and pressure in it. The dimensions and shape of the case then determine how it reacts to the pressure inside. A cases ability to mask pressure signs and achieve higher than expected performance is then called efficiency, marvelous!
You can have a small case operating at much higher pressure achieving the same vo as a larger case operating at lower pressure at the expense of less barrel life due to a larger quantity of powder being burnt. These are my observations through handloading for various cartridges, their improvemed counterparts, several custom rifles, a few wildcats, and lots of fun trying new things. Some of this post is fact, and some is my opinion based upon those facts.

 

[elkaholic]

duplicate

 

[degreen]

Looking at one of my reloading manuals it shows that in a Ackley Improved chamber to achieve the same velocity as the parent case requires more powder. Does this increase chamber pressure?

 

[Mikecr]

High pressures, and extreme pressures, can be incredibly efficient.
The trick in it is viability, and that's where roads lead to tiny underbores (like a 6PPC).

degree, an Ackley improved cartridge has a larger capacity than the parent case. More room in the boiler.
This does require more powder, and allowing more powder. Like more slower powder.

 

[elkaholic]

Looking at one of my reloading manuals it shows that in a Ackley Improved chamber to achieve the same velocity as the parent case requires more powder. Does this increase chamber pressure?

Thats because the case has more volume and you have to add powder to get back up to pressure but it doesnt mean that there isn't more to gain beyond that!

 

[elkaholic]

Efficiency is usually the claim by wildcatters used to replace the phrase overpressue. If you have to use srp brass in ur creed or 308 based case to keep primers more than 2-3 firings, you're over pressure, not efficient.

If you're manipulating case geometry to what is basically a square walked cartridge with a 40° shoulder and running high velocities than cases with 10%+ more capacity, you're not being efficient, you're loading over pressure.

We also need to establish what's over pressure? It's a personal choice I guess. You can call it efficient, I'll obviously call it another matter. Yes I've ruined brass by loading too hot in just a few firings, adg and lapua no less. I've stuck a case in the chamber that had go be driven out with a cleaning rod, it was a sherman max. I've pushed the envelope and learned a lot of things. If something sounds too good to be true, it probably is. Corners are getting cut or someone's cheating. If you want a bullet to go fast, it takes one thing, and that's the size of a case and pressure in it. The dimensions and shape of the case then determine how it reacts to the pressure inside. A cases ability to mask pressure signs and achieve higher than expected performance is then called efficiency, marvelous!
You can have a small case operating at much higher pressure achieving the same vo as a larger case operating at lower pressure at the expense of less barrel life due to a larger quantity of powder being burnt. These are my observations through handloading for various cartridges, their improvemed counterparts, several custom rifles, a few wildcats, and lots of fun trying new things. Some of this post is fact, and some is my opinion based upon those facts.

What load and what barrel on the Max?

 

[Swamplord]

Far too much emphasis on "efficiency".. what does efficiency get you ? a mini cartridge that does nothing better (in terms of velocity) over existing cartridges created 50-100 years ago, The concept is "Long Range" around here, and ELR of late ...

Velocity is key ..... BC supports velocity, in turn, the more velocity the better the bc performs, efficiency does absolutely ZERO for long range ... much less ELR ... Horsepower has always been the Holy Grail, can you imagine developing ICBM's with efficiency in mind to save on fuel and make parts (barrels) last just a bit longer and end up with short range nukes that don't make it off your continent, hahaha

Efficiency gives us 300 Savage & 7.62x39, why on earth would I want that ? It's not 1920 or 1944 anymore

Give me velocity or bust .....

 

[Mikecr]

Well, I and others I'm sure see accuracy as the most powerful ballistic attribute (not velocity).
Accuracy comes with brass & barrels that live long enough to manage it.
It comes with clean bullet release from barrels that did not recoil a bunch beforehand.
It come from full cases of the fastest yet cooler powders available.
And most of all, accuracy is not shooting until you hit your mark. It's shooting to hit your mark. It's defined by ANY single shot.

If I were trapped to fight my way out of an apocalyptic city, and given a weapon choice in 6BRA, 30-06, or 7STW,, I'd take the 6BRA without hesitation. This, because I assume it's the most accurate,, and it takes brain shots to stop zombies.