All things .308 Win

[Taudisio]

I posted this in another thread, but found the results really interesting.
I have always heard the 308 is an efficient cartridge, so I calculated it out compared to the 6 most common 308 based cartridges (and 6.5 Creedmoor and 300 Win Mag for fun). This is how much energy at the muzzle is produced per the grains of a common powder. The more efficient the cartridge, the more energy generated by a grain of powder.

I used VARGET for all 8 cartridges (it's the only powder that has data for all 8)
Max load of VARGET for each cartridge. All data is from Hodgdon's website.
I tried to pick a common medium-heavy weight bullet for each cartridge (300 Win Mag Varget data maxes at 168gr):

• 243: 100gr bullet, 33.7gr Varget, 2838 FPS, 1788 Ft-Lbs: 53.1 Ft-Lbs/Powder Grain
• 260 Remington: 140gr bullet, 36gr Varget, 2578 FPS, 2066 Ft-Lbs: 57.4 Ft-Lbs/Powder Grain
• 7mm-08: 140gr bullet, 42.2gr Varget, 2819 FPS, 2470 Ft-Lbs: 58.5 Ft-Lbs/Powder Grain
• 308: 168gr bullet, 45gr Varget, 2737 FPS, 2794 Ft-Lbs: 62.1 Ft-Lbs/Powder Grain
• 338 Federal: 200gr bullet, 47gr Varget, 2510 FPS, 2798 Ft-Lbs: 59.5 Ft-Lbs/Powder Grain
• 358 Winchester: 220gr bullet, 50gr Varget, 2445 FPS, 2920 Ft-Lbs: 58.4 Ft-Lbs/Powder Grain
• 
  
• 6.5 Creedmoor: 140gr bullet, 35.8gr Varget, 2598 FPS, 2098 Ft-Lbs: 58.6 Ft-Lbs/Powder Grain
• 300 Win Mag: 168gr bullet, 58.2gr Varget, 2964 FPS, 3277 Ft-Lbs: 56.3 Ft-Lbs/Powder Grain

As you can see, 308 generates 17% more energy per powder used than the 243 and 6% more than the 6.5 Creedmoor. The 308 is an incredibly efficient round.

What surprised me was I assumed the data would show increasing efficiency as the bore diameter increased, but it doesn't. I first made this chart stopping at .308 as I forgot about the variants with larger bores. When I added the 338 and 358 cartridges I was shocked to see them less efficient. Efficiency tops out at the 308 then goes back down!

Pretty interesting! I think another way to look at it, and a more interesting way for me personally, would be to look at the powder burned to efficiency in yards. It would definitely be more “rifle system efficiency” vs cartridge in general, and a lot more work/calculating.
For example,
308-168gr tmk, using the fastest load data from Sierra is 2800 fps from two powders avg of 46.2gr. Hits 1800fps at sea level at 650 yards. Which is 14 yards per grain.

6mm arc-95gr tmk same load data source and barrel length. 3000fps at 30.8gr gets to 700 yards. 22.7 yards per grain.

Your way is a very neat concept and a cool way to think about it though!

 

[Ajsomp]

I posted this in another thread, but found the results really interesting.
I have always heard the 308 is an efficient cartridge, so I calculated it out compared to the 6 most common 308 based cartridges (and 6.5 Creedmoor and 300 Win Mag for fun). This is how much energy at the muzzle is produced per the grains of a common powder. The more efficient the cartridge, the more energy generated by a grain of powder.

I used VARGET for all 8 cartridges (it's the only powder that has data for all 8)
Max load of VARGET for each cartridge. All data is from Hodgdon's website.
I tried to pick a common medium-heavy weight bullet for each cartridge (300 Win Mag Varget data maxes at 168gr):

• 243: 100gr bullet, 33.7gr Varget, 2838 FPS, 1788 Ft-Lbs: 53.1 Ft-Lbs/Powder Grain
• 260 Remington: 140gr bullet, 36gr Varget, 2578 FPS, 2066 Ft-Lbs: 57.4 Ft-Lbs/Powder Grain
• 7mm-08: 140gr bullet, 42.2gr Varget, 2819 FPS, 2470 Ft-Lbs: 58.5 Ft-Lbs/Powder Grain
• 308: 168gr bullet, 45gr Varget, 2737 FPS, 2794 Ft-Lbs: 62.1 Ft-Lbs/Powder Grain
• 338 Federal: 200gr bullet, 47gr Varget, 2510 FPS, 2798 Ft-Lbs: 59.5 Ft-Lbs/Powder Grain
• 358 Winchester: 220gr bullet, 50gr Varget, 2445 FPS, 2920 Ft-Lbs: 58.4 Ft-Lbs/Powder Grain
• 
  
• 6.5 Creedmoor: 140gr bullet, 35.8gr Varget, 2598 FPS, 2098 Ft-Lbs: 58.6 Ft-Lbs/Powder Grain
• 300 Win Mag: 168gr bullet, 58.2gr Varget, 2964 FPS, 3277 Ft-Lbs: 56.3 Ft-Lbs/Powder Grain

As you can see, 308 generates 17% more energy per powder used than the 243 and 6% more than the 6.5 Creedmoor. The 308 is an incredibly efficient round.

What surprised me was I assumed the data would show increasing efficiency as the bore diameter increased, but it doesn't. I first made this chart stopping at .308 as I forgot about the variants with larger bores. When I added the 338 and 358 cartridges I was shocked to see them less efficient. Efficiency tops out at the 308 then goes back down!

I’m not negating your math above. But how you define efficient to me doesn’t jive.
energy alone doesn’t tell the story, as speed is also a factor. A 243 bullet produces 84.214 FPS per grain of powder, and a 308 produces 60.822 FPS per grain of powder. So by that metric it is not the most efficient. And when it comes to killing, speed is what opens bullets, not energy.

It is far from the most efficient ballistically, and is beaten by 243, 6.5, 7mm etc.

308 is still a great cartridge for hunting, but it is not the most efficient.

 

[Elkslut]

Did a little shooting this weekend. Found a little spot u could set up a realistic hunting situation for my neck of the woods. Built a shooting position, shooting mat, bags, rocks etc. target at 640 yards. Thought I could see holes in the target but not sure, so I stuck with three shots.
Factory 1:11 twist Tikka T3 (.308 win of course) 20" with UM Reaper suppressor, in a KRG Echo. SHV 5-25. Self made arca balance. Shooting 168g pills with Varget pushing.

*Instead of dialing wind, I opted to try to hold the .4 moa it called for.

 

[proslogion]

The Echo looks really nice. I wish they had that for Rem700.

 

[Elkslut]

Ya, they are nice. The Bravo version is heavier. What I've found that I'm not a fan of is the short grip to trigger length.

 

[Macchina]

I’m not negating your math above. But how you define efficient to me doesn’t jive.
energy alone doesn’t tell the story, as speed is also a factor. A 243 bullet produces 84.214 FPS per grain of powder, and a 308 produces 60.822 FPS per grain of powder. So by that metric it is not the most efficient. And when it comes to killing, speed is what opens bullets, not energy.

It is far from the most efficient ballistically, and is beaten by 243, 6.5, 7mm etc.

308 is still a great cartridge for hunting, but it is not the most efficient.

The definition of efficiency is: The ratio of useful energy or work output to the total energy supplied (input).

Speed (velocity) is a component in the energy output calculation, but only part of it. Determining efficiency by velocity alone doesn’t make much sense. Federal has a 110gr V-Max 308 load that does 3,336 FPS. Out of a 300 Win Mag that Bullet does 3,800 FPS.

And when it comes to killing, speed is what opens bullets, not energy.

I wasn’t calculating anything about killing here, only efficiency but if you’re going to try to make an argument, Speed or expansion alone do not kill anything. Penetration kills. Expansion helps, but if you don’t penetrate you don’t kill. A 1” expanded bullet going 3000 FPS but weighting 30 grains and penetrating 2” will do a lot less damage than a FMJ passing through an animal in the same spot. Energy captures both velocity and mass, and you need both for a good shot on game.

 

[Q_Sertorius]

The definition of efficiency is: The ratio of useful energy or work output to the total energy supplied (input).

Speed (velocity) is a component in the energy output calculation, but only part of it. Determining efficiency by velocity alone doesn’t make much sense. Federal has a 110gr V-Max 308 load that does 3,336 FPS. Out of a 300 Win Mag that Bullet does 3,800 FPS.


I wasn’t calculating anything about killing here, only efficiency but if you’re going to try to make an argument, Speed or expansion alone do not kill anything. Penetration kills. Expansion helps, but if you don’t penetrate you don’t kill. A 1” expanded bullet going 3000 FPS but weighting 30 grains and penetrating 2” will do a lot less damage than a FMJ passing through an animal in the same spot. Energy captures both velocity and mass, and you need both for a good shot on game.

You need a lot less energy to penetrate all the way through a North American big game animal than most people think.