Testing, testing...

[JASmith]

...Replacing the 7.62mm with a lighter round of equivalent long-range performance is likely to be more attractive to the army (US or UK) since they are very concerned about reducing the huge burden carried by dismounted troops.
...

Tony,

We've come a long way in our community discussions!

Shifting focus to the 7.62 makes a difference, with the Grendel representing the minimum caliber and case volume that should be considered.

I'm also suspicious of the claims of superiority in 6.8. I could see the point if one is looking only at ranges of 300 meters and under combined with a fiat that the maximum size base diameter is 0.425 and that the cartridge fit within an AR15. These are all legitimate constraints for the testing -- especially if the most mature senior officials approve.

The focus on 7.62 replacement relaxes both the length and the body diameter constraints a bit.

I don't remember off-hand if the explorations in Military Guns & Ammunition looked at a 0.445" diameter body and a COAL of 2.81" but a cartridge meeting these constraints might be the best shot at an attractive 7.62 replacement for dismounted infantry. This longer overall length eliminates most of the debate over whether "green" bullets will be implementable. They exist and do well in sporting rifles with the longer cases. We will also need to contend with the consequences of the almost certain retention of 7.62X51 for aircraft and vehicle-mounted applications.

My take on the community discussions coupled with my own assessments gives me the following thoughts:

[INDENT]I am very sure 6.5 will be the optimal choice both in the analytic and test world. A reasonable study, however, would consider .25 caliber, 6.5, 6.8, and 7mm.

I am very sure that gelatin-based tests will show little or no practical difference between optimized bullets in these calibers and be close enough to that of the 7.62 M80 to count.

The M855A1 propaganda suggests that properly designed bullets in these calibers are also likely make choosing between the calibers difficult

How much a caliber improves the soldier's ability to hit in this family of cartridges will likely be the deciding factor. This favors the smaller calibers because

• Bullets of equal sectional density have slightly higher muzzle velocity in the smaller calibers for the same case volume
  
• Bullets of equal sectional density can get slightly better ballistic coefficients in the smaller calibers.
  
• Bullets of equal sectional density are lighter in the smaller calibers, reducing recoil.
  

[/INDENT]

Hope the summary is useful!

Cheers!
Joe