Testing, testing...

[stanc]

There's a theory doing the rounds of ammo development people in the UK that a long, pointed bullet will yaw more rapidly and reliably on impact than a short stubby one, because the if the bullet strikes with even a very small degree of yaw already (as most do), all of that mass much further back will make it a lot more unstable. I don't know if they've done any practical testing to demonstrate, that, though...

They probably haven't. And that theory doesn't seem supported by the wound profiles published by Martin Fackler and gel testing done by Gary Roberts and Bill Alexander.

...I think that the construction and internal weight distribution has a greater effect than the shape. Just look at the difference between the yaw performance of the steel-cored 7.62x39 bullet compared with the Yugo lead-cored.

Good examples, but I think it has nothing to do with steel core vs lead core construction. IMO, it's a result of external shape and internal weight distribution.

To look at your example above, the (steel core) M43 bullet is a long, boat tail design, with even weight distribution putting the CG near the midpoint of the projectile. The M67 bullet has the same length ogive, but being lead-core and flat base, it is short, which puts the CG more to the rear.

Another example is the 6.8mm 115gr FMJ vs 6.5mm 120gr FMJ. Both are lead-core construction (and nearly the same weight), but the 6.5mm bullet has greater L/D ratio and a more streamlined shape that -- like the 7.62mm M43 -- puts its CG close to the midpoint. In contrast, the 6.8mm FMJ is relatively short for its length, with CG more to the rear.

The long, streamlined 7.62mm M43 and 6.5mm FMJ bullets both show late yaw. The short, stubby 7.62mm M67 and 6.8mm FMJ projectiles both have early yaw.

The notable exception is the 5.45mm M74 bullet, which is long and streamlined, but yaws quickly after impact. IIRC, Fackler attributed this to imbalance resulting when the small lead plug in the nose shifts from the rapid deceleration upon impact. That type of construction probably can't be duplicated with "green" materials.