Military round comparisons

[Tony Williams]

My understanding is that going from HPBT to FMJBT reduces BC, and adding a cannelure to the bullet jacket also reduces BC. If that's so, then it seems to me that a ball projectile of the same shape and weight would necessarily have worse ballistics.

The BC is determined by two factors: the sectional density (how heavy it is for the calibre) and the shape (form factor or FF), especially of the ogive. If the calibre and weight remain constant, then the FF determines the BC. As far as I'm aware there is no fundamental reason why an HPBT should have a better FF than FMJBT. I have always understood that the reason for wrapping the jacket around the base is that this has been found to improve the consistency of performance and therefore accuracy.

A cannelure is a separate issue as that could indeed affect the FF. I don't know to what extent, nor how important the different types or locations of cannelure might be - nor indeed how necessary it might be to have one, rather than securing the bullet in the case in some other way. If one is necessary, then I suspect that placing it well back along the bullet body would have less effect than closer to the nose.

Edit to add: a bore-rider type bullet needs no cannelure anyway, as the case mouth could crimp into one of the grooves.