Complex sentence: The claims are quite contradictory as defensive rounds which expand have notoriously decreased penetration by their nature, whereas more mundane practice rounds penetrate further but have decreased stopping power--penetration and expansion are opposites and designs must trade one for the other.
Split into simpler sentences: The claims are quite contradictory as defensive bullets which expand have notoriously decreased penetration by their nature, whereas more mundane practice rounds penetrate further but have decreased stopping power. Penetration and expansion are opposites and bullet designers must trade one for the other.