Understanding cartridge efficiency

[dfanonymous]

 

[Mikecr]

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.

This is right.

If you were to neck up a 25wssm case to 30cal, and nothing else, it would match a 308 in capacity, and it would produce higher velocities with the same loads and barrel lengths. I guarantee it.
WSSM can be THE example of short/fat efficiency, and this attribute is adjusted with 'weighting factor' in QuickLoad.
Weighting factor is a setting designating ability to burn powder in the case -vs- half way down the barrel.
Inefficient cartridges produce and project a powder slug on the back of bullets, delaying/preventing burn, and adding to recoil.
A 30-06 being pretty much worst about this, a 30wssm would be among the best (for 30cal & with 30BR).

For calibration of proposed 30wssm, weighting factor WILL have to be adjusted, and with no other changes QuickLoad's output MV will go up, and muzzle pressure will go down. I had to do this with a 26wssm IMP to calibrate. It is is more efficient than any 26cal cartridge in production.
Ackley improved cartridges are designed to hold back the powder. It would be appropriate to adjust QL weighting factor for them. But AI is also applied to cartridges that would not be very efficient even with it. The benefit there is a little better reloading life. A 30-06AI would not benefit much from the efforts.

The price for short/fat design is that you need to design the gun for it. If you don't, the effort will cause problems and fail w/resp to gains. From what I saw with it, Savage was the first gunbuilder to understand this. Winchester and Browning were not, and Remington never would get it..
I would recommend a Savage WSM or WSSM gun action to begin a project with that case.

 

[25WSM]

No way in heck the Dasher does what a 243 can do. If you take a 22 inch barrel 243 with factory loads and compare it to a 30 in Dasher run hot then yes it does but that's a skewed comparison. In the same length barrel the 243 outruns the Dasher by 200 fps. Put rl26 in the 243 and it will outrun it by 400 fps. Not even close. My 6slr is slightly less capacity than a 243 and it will push a Berger 108 3400 easy with rl26. It actually topped out at just over 3450 before bolt lift got harder. Be hard to get a Dasher much over 3000 with a 108. A better comparison is how a 6bra can almost keep up with the Dasher with a much shorter powder area. I really wish someone would come out with good wssm brass. I really like them little boogers. I think a fast twist 25wssm with 131s would make a heck of a long range rifle.
Shep

 

[358 Guy]

If you have 2 similar capacity rounds, both loaded with the same powder charge and bullet, and all others things being equal ( barrel length. The one that produces higher velocity consistently, is probably more efficient if pressures are near equal. As in petroleum burning engines, the shape of the combustion chamber has a lot to do with it. If I can burn less powder for equal performance, that is probably the round that I would go with. Lower powder charges also mean greater barrel life.

 

[Rich Coyle]

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:

Here's a little tidbit to follow your post. I had a brand new Savage reamed and a brand new custom Blackstar barrel on a Remington action reamed with the same reamer for my .220 Extremist. Both with 26" barrels. The Savage averaged 4,005 feet per second with fifty-five grainers while the custom barrel averaged 4,300 fps from the same box of ammo. The Savage always fired three shots in the high .3's and the custom barrel hardly ever managed to get below 1" at 100 yards.

 

[highdrum]

What load and what barrel on the Max?

26" proof sendero 7max, 180hyb @ 3150 w/ 66.5 rl26 case was stuck solid, bolt removed part of rim during attempt to extract prior shot w/ 66gr saw very little if any pressure signs. Also 69gr N570 w/ 195eol @ 2995fps, primer basically fell out, this was 1st firing after forming brass.

 

[Opa-lopa]

Only a few things go into making MV for a given bullet: peak pressure, powder type & charge weight, chamber volume & in-bore travel distance. If interpret your question correctly, you want to know if the shape of the case or some other detail in the cartridge design results in more MV if all the other factors are held constant, is that correct? I'd tell you it'd be tough to prove one cartridge has better "efficiency" than another, all else being equal. If it amounted to more than 25 FPS out of 3000, it would surprise me greatly.

 

[DavidleeCole]

Would a better comparison every thing the same a 5.56 or .223 from there is only a little bit of difference in the case llike a few thousands right.

 

[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.

removed

 

[berg1985]

So if a 300 wm can push a 180 at same speed as 30 nosler using 4 gn less powder I would say yes that makes a 300 wm more efficient then a 30nosler, how about comparing a 7SS to a 7Saum should be very close case capacity

OK, that is much better, but they do not have the same case capacity (.30 Nosler has the edge, it also varies from brass manufacturer). Below is a test extracted from another site but he is also a member here ...

View attachment 196523

At least we are on to something. If you do a search BROZ did a comparison between the two. The efficiency between the two is purely relative to the end-user.

The .30 Nosler vs .300 Weatherby (in terms of case capacity, but of course varies in brass manufacturer) might be a better comparison.

View attachment 196524

 

[elkaholic]

26" proof sendero 7max, 180hyb @ 3150 w/ 66.5 rl26 case was stuck solid, bolt removed part of rim during attempt to extract prior shot w/ 66gr saw very little if any pressure signs. Also 69gr N570 w/ 195eol @ 2995fps, primer basically fell out, this was 1st firing after forming brass.

Thats why I asked what barrel. Proof has been replacing one after another for this very reason!!
Ive had several clients blow primers 3-4 grains under max!
Some aren't bad enough that people even know that there is a problem, they just think they have a slow barrel.
I havent posted about it because I don't like doing that but I guess its time. To their credit, they are replacing MANY barrels!

 

[25WSM]

What is wrong with the proof barrels? Why are they building pressure in spikes. How is Proof the number 1 barrel used in PRS if there are so many issues?
Shep

 

[XSIVSPD]

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

It's interesting to me that in the first 2 pictures (7saum and 280ai) the 7 has a 0.4 grain h2o advantage in capacity, but the 280ai max charge is 0.5gr higher.

Yes, I know seating depth will cause this, but it's interesting to see in print what can happen

 

[bigngreen]

What is wrong with the proof barrels? Why are they building pressure in spikes. How is Proof the number 1 barrel used in PRS if there are so many issues?
Shep

They have been having issues as of late being spikey and pressure issues.
PRS guys are dropping them like hot potatoes right now!! It's why your seeing Bartlein and so many others getting in the carbon game!