Didn't ask for any in the first place!

...but thanks for offering mhb.

Perhaps I should clarify once again that there were NO puzzles here, nor problems to solve, simply an experience documented for the interest of others. The rifle in question is a marvellous scrub-gun, it WORKS, and doesn't need any improving. It was built with a 'free' barrel with the knowledge that it probably wouldn't stabilize 300-grainers, but that 270, 250, and even 235-grainers were available in that calibre, at increasing MVs, and a good working-load would be developed accordingly. The fact that the 285-grainer won't remain stable at longer ranges is entirely incidental and was offered simply to add to the corporate knowledge.

Thanks for the measurements on the Grand-Slam bullet CB, appreciated. Interestingly, the theoretical twist rate for that bullet, according to the Calculator I posted, is 16.9 inches. My barrel is unlikely to be slower than that! I'll measure it tonight.

This mole-hill mountaineering looks destined to continue....