The only semi-auto I did any significant cast boolit work with was the SKS. My notes show the best load with a cast boolit was only a grain below starting for an FMJ of the same weight (155) and powder (4895).
Of course, 7.62x39 isn't 270 Win when it comes to velocity or pressure.
Here's the only cast load shown in Lyman's #46 for 270 Win:
Of course, 7.62x39 isn't 270 Win when it comes to velocity or pressure.
Here's the only cast load shown in Lyman's #46 for 270 Win: