FMJ yaw and upset performance

[Tony Williams]

Tony:

This one shouldn't be too hard to figure out. How much better does the 6.5mm bullet have to be before it shows a quantum improvement in exterior and terminal performance?

Start out with defining what that quantum improvement is and the rest will be easy to solve -- on paper.

What must the BC and velocity be to match in exterior terms and then multiply by about 50% before anything can be proven in real terms. When that is solved, then look at powder technology and finally bullet construction.

LR55

My approach is a bit different: I would start with the bullet, because its characteristics are the key to the success of any new round. There are two main aspects to this success:

1. Terminal effectiveness, in terms of straight-line penetration through various intermediate barriers (including car windscreens, a real headache for 5.56mm) plus rapid and reliable yaw and bullet upset on impact (I'd like to see the bullet begin to yaw within a couple of inches of penetrating a body, and completely turn over in order to travel backwards within 12 inches).

2. Exterior ballistics, in terms of a rate of velocity loss significantly less than 7.62mm M80 (probably around 0.50 BC).

With the bullet design settled it would then be easy to work back from the requirement to match the retained energy of the 7.62mm M80 at 1,000m, in order to decide what the muzzle velocity needs to be. The next stage would be to calculate the propellant load to achieve this MV in a specified barrel length, and therefore the case capacity, and finally the form of the cartridge.

This approach could be applied to any calibre, of course, but I think that the 6.5-7mm range looks the most promising. A 7mm round would probably show more reliable terminal effectiveness than 6.5mm at the cost of more ammo weight and recoil, and a steeper trajectory; you pays your money and takes your choice...