How effective would osmium bullets with a steel core be?

I would think it would be terribly less effective. Assuming you have already found an economically large amount and efficient method of producing bullets, there are lots of hurdles here. read more

Osmium is extremely hard, as hard or harder than the steel of the barrel you are using. So firing Osmium bullets (without a teflon coating or equivalent) would cause throat erosion and excessive barrel wear very quickly. read more

The lead core then expands against the steel core causing the bullet to burst in the middle around the cannalure. The purpose is to fragment the bullet into; the jacket, the lead core, and the steel core, all going in different directions. read more