Understanding cartridge efficiency

[zb338]

How about the .280 and the 7MM AI. ?

Zeke

 

[FlyGuy11]

This shows me that we all have been quarantined too long
This is just my $.02 on the subject.
Benchrest shooters use short, fat cartridges with higher shoulder angle for "higher efficiency" and P.O. Ackley used it for the same as well as longer case life. The WSMs were developed based on the efficiency logic gained from benchrest shooters (maybe a little PO Ackley influence). I have personally found that a reloader selecting the right bullet and powder for the best result is the best solution. I have a 280 AI and it will get a berger hunting 168gr to 2952 fps (25" barrel 1in9") with Reloader 26. I can equal or kick a 7mm Rem Mags butt 168 gr and below bullets. Raise the bullet weight to 175gr or 180gr the 7mm Rem Mag kicks my 280 AI's butt.

How I select a cartridge is based on desired energy at a desired range with reasonable wind drift. What do I know I drank some Kool-Aid and bought a 28 Nosler rifle for Elk hunting. Zero to 900 yards I don't worry about efficiency due to considering this a dedicated low round count purpose hunting rifle. And my Kool-Aid tastes great.

 

[Jfightingfalcon]

I think the discussion really boils down to what people perceive as efficiency. To most, I suspect it's when they put X grains of powder into one case and move an identical bullet through an identical barrel a given number of feet per second faster (and without SIGNS of excessive pressure) than if they ran that same powder charge in another case. Is this efficiency? Scientifically speaking, no doubt: getting more kinetic energy from the same reaction. However, to a reloader, the real question lies in where the bonus kinetic energy is coming from. Does this hypothetically more efficient case manage the pressure curve better, or does it produce more pressure with the same powder charge. If I may voice my rather inexperienced opinion in this gathering of veterans, I strongly suspect it's the latter, and the only real advantage of 'modern' case designs (ballistically speaking, I understand magazine length, ease of reloading, etc) is their ability to produce and tolerate higher pressures, thereby generating more velocity. Unfortunately the equipment required to properly test any of our theories is prohibitively expensive. Besides, what would wildcatters argue about?!

 

[FlyGuy11]

Guy on the left is the Kool-Aid drinker with the Kool-Aid rifle.

 

[Plinker147]

Depends on how you define efficient. I see is as getting more or the same for less. So in terms of cartridges comparing to cartridges with same case volume doesn't really fit like 7SAUM and 280AI. Basically the same ballistics, difference will be in the platform design not the cartridge.

Now if you compare a 6.5 creedmore to a 6.5-06 both built in "saami" specs with 24 in barrels The 6.5 creedmore can achieve near same velocities with 5-10gr less powder, more efficient, less powder burned for same or very close to same results. You can tweak the platforms so the 6.5-06 will shine but always at the expense of more powder. Creedmore more efficient in power used for results.

Look at 6 creedmore compared to 6 BR. A 26-28 barrel on a BR throated correctly can keep pace with a "spec"22 inch Creedmore. Burning less powder and twice the barrel life. Platforms aren't the same, But barrel life and cost per shot are in favor of 6BR making it cost efficient for like results.

All depends on how you want to look at efficiency

 

[Stiltsville]

It keeps getting better. Now we have a guy with a 280 AI saying it's faster w/light bullets than a 7 mm RM. It cannot be as more powder in the same bore size always equals more velocity. I'm waiting for the guy with the 338-06 AI to tell us it's faster than the 338 RUM.

FYI in Loaddata.com the fastest 100 gr load in the 280 AI is <3550 fps, 7mm RM
is >3700 fps.

 

[corsair4360]

I have analyzed this and came up with a term "overbore index" which is the capacity of the case in grains divided by the area of the bore in inches. For 7mm cartridges here is a bit of the analysis:

Name	Bullet	Case length	Rim	Base	Shoulder	Neck	OAL	Case Cap	Overbore Index
7mm-08 Remington	0.284	2.035​	0.473​	0.470​	0.454​	0.315​	2.800​	47.8​	755​
7×57mm Mauser	0.284	2.244​	0.473​	0.472​	0.430​	0.324​	3.060​	54.3​	857​
.284 Winchester	0.284	2.170​	0.473​	0.500​	0.475​	0.320​	2.800​	66.0​	1042​
.280 Remington	0.284	2.540​	0.473​	0.470​	0.441​	0.315​	3.330​	68.0​	1073​
7mm Remington SAUM	0.284	2.035​	0.534​	0.550​	0.534​	0.320​	2.825​	69.2​	1092​
.280 Ross	0.284	2.590​	0.556​	0.534​	0.404​	0.317​	3.500​	76.0​	1200​
7mm WSM	0.284	2.1	0.535	0.555	0.538	0.321	2.850​	76.8	1212​
7mm Remington Magnum	0.284	2.500​	0.532​	0.512​	0.491​	0.315​	3.290​	81.4​	1285​
7mm Weatherby Magnum	0.284	2.550​	0.530​	0.511​	0.490​	0.312​	3.250​	85.0​	1342​
7mm STW	0.284	2.850​	0.513​	0.532​	0.487​	0.315​	3.600​	92.6​	1462​
7mm RUM	0.284	2.850​	0.534​	0.550​	0.525​	0.322​	3.650​	108.1​	1706​

This may help some, infuriate others, and cause others to contemplate...

 

[FlyGuy11]

So again choose the right bullet and the right powder 280 AI wins; change the powder the 7mm Rem Mag wins. To me it's splitting hairs. I have dropped Elk with the 280 AI at 422 yards 1 shot so I don't think the Elk cared about efficiency.

 

[Terry Balding]

Your question missed the mark. Effency is about more with less. The .243 and the 6 Dasher is a good example. The Dasher can do what the .243 does with less powder. That's effecient.

 

[JWM]

A more efficient case will give more velocity with the same powder charge, bullet and primer, or the same velocity with less powder, if the term means anything; and possibly better accuracy potential from more consistency. Or, without the condition of the same case capacity, a .223 is more efficient than a .220 swift, because you get roughly 2/3 of the velocity with half the powder. That's the law of diminishing returns. A major factor in efficiency is how much powder follows the bullet down the barrel, you have to accelerate that additional weight, too. A short fat case with a sharp shoulder should burn more of the powder in the case, less in the barrel, and be more efficient. Some use primer tubes that start the powder burning in the front half of the case for the same reason.

 

[FlyGuy11]

Your question missed the mark. Effency is about more with less. The .243 and the 6 Dasher is a good example. The Dasher can do what the .243 does with less powder. That's effecient.

So the AI with the right powder gets 7mm Rem Mag velocity with less powder. Yeah I think I am tracking efficiency based on my first post stating that the purpose of WSMs was using a short, fatty for a theorized more even efficient powder burn. As lessons learned from the Benchrest folks. In the end pick what meets your WEZ-Weapon Engagement Zone.

 

[Stiltsville]

I've gotta move on. This case shape BS has been buried over and over, yet some still cling to it.

One last time, the same powder charge in cases of equal capacity will produce the same velocity. End of story as Handloader proved in a lab.

All you true belivers should read this: https://gundigest.com/gear-ammo/ammunition/ammo-case-shape-matter

I gotta go load some subsonic 300 B/O in case the riot comes here.

 

[Stgraves260]

Well an example would be a 260 and a 6.5 creedmoor have SIMILAR cases but different cartridges don't tend to be exact...in my example of the creed and 260 rem, they are different, or they would be the same cartridge which they are not.

You are going to have to give specific cartridges to compare if you want any serious input. Not that it's impossible but I can't think of any caliber specific case that is the same as another cartridge but not that cartridge, and one is better than the other.

I don't understand. The 260 has 53.5 gr H2O ( Remington Brass ) and the 6.5 creedmoor has 52.5 gr H2O. ( Hornady Brass ) I do have Hornady brass for my 260 and my 6.5 Creedmoor and the 260 has 2 gr H2O more than the 6.5 Creedmoor.

 

[FEENIX]

I was thinking "ahhh no...FEENIX got em on the first post of the thread." Lol

I'll hold my popcorn gif depending what happens.

How about now?