07-08-2011, 09:44 AM
Okay, let me see if I have the whole picture right.
We need to get a worthwhile reduction in ammo weight, while having significantly better terminal effectiveness than 5.56x45 in close combat, with terminal effectiveness at long range -- and barrier penetration at all distances -- comparable (if not equal) to 7.62x51.
In addition, for psychological reasons muzzle velocity must be equal to that of 7.62x51 ball, when fired in barrels of the same length: 2700-2750 fps in a 20" barrel. Plus, it must be done using "eco-friendly" bullets, with steel and/or copper as core materials.
In order to get the necessary weight reduction, the cartridge case has to be of significantly smaller diameter and (probably) shorter length than for 7.62x51. On the surface, this appears feasible. The weight comparisons I did on the previous page show that 100 rounds of linked 7x46 provides a 25% weight reduction, and 6.8x43 cuts weight by 35%. IIRC, that's close to what the early LSAT goals were.
The bullet also must be substantially lighter than the standard 7.62 ball projectile, but be very streamlined, with a long ogive, so as to have a high BC for maximum downrange velocity and energy. Unfortunately, with a non-lead core, such bullets are extremely long, with undesirably high L/D ratios that may make a matching tracer (which is typically longer than the ball round) too long to be viable. Then there is the reduced powder capacity to contend with, too. If the bullet is shortened enough to solve those problems, then BC is greatly reduced. Plus, the lighter the bullet is made, the less effective it will be against both soft and hard targets.
I used to think this concept was doable, if just barely. But, after the last couple days, I'm beginning to think it may not be.
We need to get a worthwhile reduction in ammo weight, while having significantly better terminal effectiveness than 5.56x45 in close combat, with terminal effectiveness at long range -- and barrier penetration at all distances -- comparable (if not equal) to 7.62x51.
In addition, for psychological reasons muzzle velocity must be equal to that of 7.62x51 ball, when fired in barrels of the same length: 2700-2750 fps in a 20" barrel. Plus, it must be done using "eco-friendly" bullets, with steel and/or copper as core materials.
In order to get the necessary weight reduction, the cartridge case has to be of significantly smaller diameter and (probably) shorter length than for 7.62x51. On the surface, this appears feasible. The weight comparisons I did on the previous page show that 100 rounds of linked 7x46 provides a 25% weight reduction, and 6.8x43 cuts weight by 35%. IIRC, that's close to what the early LSAT goals were.
The bullet also must be substantially lighter than the standard 7.62 ball projectile, but be very streamlined, with a long ogive, so as to have a high BC for maximum downrange velocity and energy. Unfortunately, with a non-lead core, such bullets are extremely long, with undesirably high L/D ratios that may make a matching tracer (which is typically longer than the ball round) too long to be viable. Then there is the reduced powder capacity to contend with, too. If the bullet is shortened enough to solve those problems, then BC is greatly reduced. Plus, the lighter the bullet is made, the less effective it will be against both soft and hard targets.
I used to think this concept was doable, if just barely. But, after the last couple days, I'm beginning to think it may not be.