Casting soft noses can be done, but two pots are needed, and the exact temperatures - AT POURING - are vitally important to get seamless joints. I did it for a short period in testing some .375's and .430's, but gave up as too much hassle- to many rejects which now have pure lead stuck to the alloy so you can't just dump them back in the alloy nor the pure pot.

Since 1,000gr. is pure lead weight for a 7 bore ball at .873" - could your 1,020gr. ball be groove diameter for a slightly oversize 8 bore?