mhb:
The 285-grainer was sufficiently stable at the muzzle, in fact sufficiently stable out to beyond 50 metres. Your inference was that if a bullet starts out stable, it would stay that way. Not necessarily so.

That particular rifle was experimental, in that I got the barrel basically for the cost of the gunsmithing, knowing that the twist-rate was optimum for .375 H&H velocities, but willing to 'have a go' to get the most grunt possible out of a 'Smelly'!

Even if I had to step back to the 250gr Sierra boat-tail (lovely bullet, but soft) it would still be a great scrub-gun for hogs.

Can't remember the twist-rate offhand, so will have to re-measure. Bog-standard for the H&H cartridge though.