Some time ago, a Gun Digest, or perhaps Guns and Ammo Annual had an article on casting and loading ZINC bullets in the .458Win, Mag., along with or another article on shooting 220gr. .308 bullets in a .458 Mag, using nylon 'sabots' turned (at slow speed) on a lathe. Their 220gr. bullets were hitting point on, so I assume a 14" or 15" twist at the just over 3,000fps the author was achieving.

The extremely light weight zinc bullets, between 100 and 200gr. were being shot with horrifically fast pistol or maybe shot gun powders and some achieved speeds over 4,000fps.

Throat life unknown but possibly short?

At the time, I experimented with the 220gr. bullets and nylon sabots when I lived in Smithers (in 77 or 78), but did not have much success with them - point-on impacts (15" twist x 22" McGowen tube) but huge 6" groups at 100yards and were running close to 2,950fps,IIRC? I had my own Oehler M12 chronograph with sky screens at that time.

These were tested in my first .458 - the one I used for 15,000 rounds - grouse to moose. I retired that barrel in about 2005 - again, iirc. Sometimes are as sharp and clear as to dates, while others slip off into obscurity.