I have read several places that there's a way to calculate the optimum caliber for every cartridge.

Is there such a formula?

What is meant by optimum?

Thanks

Usually "optimization" refers to some (input) variable that can be changed, and the output can be checked for change. The optimum occurs when the output peakd: is is less below and above teh peak.

Most cartridge design variables show rising output with incresing input (like powder charge weight), you don't encounter peaks and valleys in the output, except for accuracy (which varies from rifle to rifle anyway).

I don't know of any formula that will tell you the "optimum" caliber for any given cartridge case. Optimum seems to be a word captured by marketeers.

jim

If you see what the BR guys use. They have the 6PPC wich is optimal for 1-200 yards br, while they use a 6br for 600 yards. Both are 6mm but one use 60-70grain, the other 105 grains.

You have to state the use first.

Here is some funny reading: http://www.reloadersnest.com/article_shoulder_angle_oct2603.asp

Cartridges of the World reports that the US Army developers of the 6 mm Squad Automatic Weapon cartridge were the first to use computer parametric analysis to design a cartridge.

They ended up with a .410" cartridge head, and a length of 1.779". The bullet was a 105 gr FMJ BT.

jim

optimum bore ratio, not caliber...

phrases like "over bore" and "underbore" come to mind...

the 38-55 under bore...

7 stw ... so far over bore it's not funny...

but I can't rember what the calculation is

jeffe

Kind of a funny thing. If you have a set of performance characteristics I could see coming up with the cartridge that best matched it, but take the 7mm STW for example; if you want a 140g to go really fast, and penetrate with the SD that a 7mm bullet will give, then it's hard to find a more optimal case.
The 308W is a very "optimized" round, but it just ain't very optimal for shooting 180g bullets very far.
Expansion ratio is a useful figure, to compare rounds of a known ability. When we say the 505G has near the same expansion ratio of the '06, it tells us that for similar barrel lengths it can make similar use of its powder capacity. The Lapua, on the other hand, needs about a 30" bbl to get the expansion ratio of a 20" '06 rifle. Not sure if that helps you.

I checked the statement that got me started. Bore is the correct term that was used.

The quote is".. every bore diameter has an optimum bullet weight/case capacity for optimum efficiency. . ."

That's the formula I'm trying to find.

Thanks

John

quote:

Originally posted by Bwana-be:
Kind of a funny thing. If you have a set of performance characteristics I could see coming up with the cartridge that best matched it, but take the 7mm STW for example; if you want a 140g to go really fast, and penetrate with the SD that a 7mm bullet will give, then it's hard to find a more optimal case.

BB,
it's on teh other side of optimized... when you add 1gr of powder to a 708, you get X fps... when you add 1gr to a STW youget <X fps ...

and works the same in percent, too, which is worse

the stw is way overbore.. which means ineffceint

jeffe

The new 6.5x47 is optimized for a 100-125 grain bullet.

quote:

Originally posted by I Bin Therbefor:
I checked the statement that got me started. Bore is the correct term that was used.

The quote is".. every bore diameter has an optimum bullet weight/case capacity for optimum efficiency. . ."

That's the formula I'm trying to find.

Thanks

John

John,

Efficiency in rifles depends on application. If you are a target guy it is accuracy; if you are a hunter it is most often velocity, sometimes a combination of velocity and accuracy.

For example I used to shoot benchrest with a 6X47. Loads were a full case of powder with a hand-made 62 grain bullet. I really did not care about velocity at 100 and 200 yards, group size was all. As I recall my best barrel was a 12" twist.

I hunted with a 6 mm too, but it was a 6 mm Rem with 100 grain Nosler Partition bullets. I use a 9" twist barrel.

Did your author specify the application?

There has been no end of arguing over the years about what is the optimum for a particular bore, conside thte .30 cal today. You can go from 7.62X39 to .30-.378 in factory guns.

jim

Jeffe, you're tslking about "optimum efficiency."
One of his questions was, "what is meant by optimum?"
If it's a set of performane standards, e.g., 140g .284" at 3300 fps, it is of no import that a 7-08 can do less more efficiently!
;-P
I guess a scientific appraoch would be to see when the powder charge increase caught up with the performance increase, but I bet that happens before the 7mm-08.
We might say the 7-08 gets about 60fps per grain with 140g and the 7mm Rem about 45 or so.
But the 7mm BR would give us about 70fps per grain! But for most of us a 140g at 2100 fps isn't "optimal" by any means....

"every bore diameter has an optimum bullet weight/case capacity for optimum efficiency"

Efficiency I took to mean powder burned. What if you simply divided powder burned in grains into energy of the bullet at the muzzle? You'd get lbs/grain. If you did that for a variety of bullet weights and powder burned combinations for the given bore, wouldn't you find the max lbs/grain for each combination? The combination that gave the most lbs/grain would be called operating at "optimum efficiency". Whole bunch of assumptions behind that reasoning, but still might be interesting.
I did find the site for the quote and am going to email the author. As I'm quoting him without permission, I'd like to get his response before I say a whole lot more.

Thanks for all the responses.

John,

It will be interesting to hear what the author says...jim

Yeah, I'd like to hear what he says too. But even more, I'd love for someone with too much time on their hands to do what you propose, and find some optimum calibers and bullet weights for the major cases (308, '06, Win Mag, FL belted, 404, Rigby) - might be easy with quickload to some up with some pseudo-data for funzies.
What if it turns out the 30-30 beats them all? :-P

Purely for purposes of discussion, let me put these generalizations forward and see what you all make of them. Tear into them, teeth, claws, and logic - the idea is to get us thinking outside of the box.

1) Efficiency. Smaller cases tend to be more efficient, i.e. you get more fps per grain of powder. That's great for target shooters, but isn't much help for hunters.

2) Practicality. Each case has one bullet which it shoots most effectively. We have to assume that each has the correct rate of twist and barrel length to achieve greatest efficiency with the chosen powder. Just to think about it, not because I think the stated examples are necessarily correct, let us look at a possible .30cal baseline: .30carb - 110gr; 7.62x39 - 125gr; .308 - 150gr; .30-06 - 165gr; .300mag - 180gr.

3) Accuracy. Short, fat cases with sharp shoulders are more inherently accurate than other bottleneck or straight wall cases. (There is a fancy interior ballistics theory for this, and it seems to make sense.)

Only generalization #2 seems to offer any real help to hunters, but it is the hardest to justify either by logic or by experiment. I am leaning towards the opinion that only target shooters can rely on the notion of "optimal loads" (at least in terms of efficiency), while hunters can at most calculate the best bullet for their twist rate and find the best accuracy by trial and error. What do YOU think?

I doubt there's any 'optimal' caliber. Take my .240 Incinerator for instance. It's a 6mm on a .264 Mag case and it pushes a 70 gr Ballistic Tip to 4,400 fps (28.5" tube). It's horribly over-bore, burns a ton of powder, and wears our barrels. In spite of these qualities, it cut's sub 1/2" groups at 100 yards. So with respect to accuracy and speed, it's pretty optimal.....now if efficiency is brought into the mix, it doesn't shine quite as bright.

Lee Martin
www.singleactions.com

how about if it is a big bore and cant burn all the powder in a 22" tube its overbore if its a medium bore and it cant burn its powder in a 24" tube... small bore 26" is that not somewhat of a good rule?