Rifle Cartridge Efficiency Formula

[mitch260]

Yes you are correct, but when discussing the 2, BC is referred to as external ballistics and SD is referenced as a way to summise if a bullet will penetrate, which is terminal ballistics.
I stand by my statement.

Cheers.
gun)

I was not disagreeing with you, I just wanted to point out that SD and BC are not independent of each other when referring to external ballistics.

This whole conversation is dependent on what kind of efficiency the OP was referring to.

Most of the time a cartridges efficiency is referring to ballistic efficiency which is a matter of internal ballistics and is a figure based on factors like amount/type of powder, bullet weight, bullet start pressure, muzzle energy, etc.

Once the bullet leaves the barrel, it is no longer a matter of the cartridge's efficiency, but of a bullet's weight, SD, form factor, etc. So in other words, the bullets "efficiency".

 

[375rifleman]

I`m currently in the process of designing a rifle wildcat and am trying to make the most efficient cartridge possible.

 

[Mikecr]

JaseinMT nailed it for internal ballistic efficiency. You would design an underbore cartridge along the lines of a 6PPC, 30br, and up to almost ~6.5x47L. Any larger isn't viable, and with increasing compromise.
mitch260 nailed it for external ballistics.
Terminal ballistics is more philosophy than ballistics..

Balancing the two ballistic attributes is just what wildcat designers have been doing forever.
But usually with a theme(competition, large/small game hunting, Hollywood, etc).
True, middle of the road to me, would be something near a 26wssm Imp/140 VLDs/3kfps.
Short of dangerous game, it would kill anything at distance, with little powder.

 

[davkrat]

I`m currently in the process of designing a rifle wildcat and am trying to make the most efficient cartridge possible.

Well you really need to decide what you want the gun to do. As Mikecr pointed out likely the most efficient cartridge will be one of the low power bench chamberings. Not really much to write home about if the intended target is larger big game animals. I think you need to look at what bullets have the highest BC and SD then compare the speeds that various cartridges can launch them at. Most likely something in the .260, 6.5mm or 7mm range will be the best bullets on paper. But perhaps a .308 launching 215 gr Berger out of a 32" tube would be more efficient.

Honestly I think what you need to do is identify some classic cartridges that fit the bill of what you are likely to use the cartridge for and then start weighing the compromises between more powder/recoil, barrel length, barrel life, minimum velocity/energy at range, etc. Identify which of those compromises you can live with out and which ones you really need. I think you could pretty easily make a little model comparing your wildcat to a standard. You could then weigh the differences plus or minus for the various factors. I honestly think only you can decide what compromises to make with your cartridge.

 

[davkrat]

PS - according to this chart from Berger the only bullet better in the SD and BC department than the 7mm 180 is the 300 grain .338 Hybrid.

http://www.bergerbullets.com/wp-content/uploads/2011/05/formfactors_chart2.gif

 

[mitch260]

PS - according to this chart from Berger the only bullet better in the SD and BC department than the 7mm 180 is the 300 grain .338 Hybrid.

http://www.bergerbullets.com/wp-content/uploads/2011/05/formfactors_chart2.gif

That is a slightly outdated chart. The .308" 215gr and 230gr hybrids are also better in both departments than the 180 grain vld's or hybrids.

 

[Mikecr]

It is true that all ballistic designs begin with the bullet. Everything is built around it.
Also, beyond tactical, accuracy is the most powerful of attributes.
And in the long run, cartridge designs that are sustainable in a shooting system, are more accurate.
Finally, there is field function/practicality.

So it's not enough to just pick a highest BC bullet.
The next question would be; 'can the bullet be released accurately?'
And the next question: 'how long can that accuracy last with it?'
Then; 'is there any real world use for it?', 'what does the real world need?'

When you break it down like this & plot it out, you'll go right past the big boomers, and past tiny underbores, and you'll ignore all things 'tactical'.
You'll end up at mid-cal and at correct capacity(not highest) for the chosen bullet weight.

Once you've studied all the cartridge design books, and set yourself up with the best in design software, and the best in reloading tools,, it's not difficult really, but time consuming.
There will never be a single formula.

 

[davkrat]

Yep and you'll probably end up with something in the .260, .270. .30-06 or 7mm Rem Mag range. More than one way to skin a cat and most any of them will work.

 

[mitch260]

If you (the OP) are going to make your own wildcat, I would highly recommend that you get QuickLoads and QuickDesign. Although it isn't 100% accurate and shouldn't be used as such, it can help you do a lot of experimention in little time. It can go along ways to help you get the most out of your wildcat.

 

[antitactical]

I've been under the assumption that short fat is more efficient. I was reading the other day about a 300 wsm vs. A 300 H&H. Both have the same volume roughly and they can interchange load data. The kicker is they produce the same velocity and accuracy within the reason ( a fast barrel vs a slow barrel) the h&h is long ,tapered ,and has a sloping shoulder (all supposedly inefficient) and the wsm is short fat and a sharper shoulder. It should take the same amount of powder and give you 100fps due to its efficiency. It's something to ponder. Im not saying a 30br, ppc, 222, and .308 aren't efficient. The case shape changes with them too.