FMJ yaw and upset performance

[stanc]

IMO, some of the wound profiles shown below give a good idea of what's possible for non-deforming bullets.

To achieve early onset of yaw, it seems necessary to have rearward weight bias in the projectile. There appears to be two ways to achieve this:

1. A long-for-diameter, streamlined bullet -- such as 6.5 Grendel -- needs an air space in the nose. See 5.45x39 M74 profile for example.

2. In a short-for-diameter, not so streamlined projectile -- such as 6.8 SPC -- an air space in the nose in not so vital; the bullet shape seems to "want" to yaw relatively quickly after impact. See 7.62x39 M67 profile. (The Yugo M67 is a lead core, flat base bullet that is shorter than the original Russki M43 steel core, boat tail design.)

Terminal Performance

I have found only a few test results of 6.5mm and 6.8mm FMJ ammunition.
Awhile back, Silver State Armory tested a 6.8mm 101 grain "penetrator" that was reportedly of the same steel tip/lead core configuration as 5.56mm M855.

As shown above, the 6.8 FMJ (101gr M855-type) displayed pretty good terminal effects after punching through a thin steel plate. However, when fired into bare gel, wound profile was reportedly little or no better than for M855.

Attached: Gel tests of 6.5 Grendel 120gr FMJ and 6.8 SPC 115gr FMJ, both with lead core bullets. Note that the 6.5mm bullet was neither developed for the cartridge, nor designed to yaw, which explains the undesirably long (7") neck. The 6.8mm projectile had better (3") neck length, but still longer than the (>1") ideal.

Conclusion: Designing a streamlined, non-deforming, non-fragmenting, 6.5mm bullet that -- when fired at Grendel velocities -- will deliver terminal performance substantially superior to 5.56 NATO seems likely to be a great challenge.