some bullets are "hollow points" which are made for expansion
other bullets are "open tip match" which is really a byproduct of a manufacturing decision. i.e. forming a cup of copper and pounding lead into it as a mfg process means you can either have a nice base or nice tip but not both. for accuracy, the uniformity in the base of the bullet is more important than the tip, so the decision is essentially to wrap the copper around the bottom and then use a die to squeeze it together at the top, which still leaves a slight open spot. i.e. the open tip is not designed to expand.
just personal opinion, but i think those rounds have a reputation for effective killing not because of some magic expansion, but because they are a rifle round and because people hit their targets more often with them because the people that use them tend to practice more and are more accurate shooters
other bullets are "open tip match" which is really a byproduct of a manufacturing decision. i.e. forming a cup of copper and pounding lead into it as a mfg process means you can either have a nice base or nice tip but not both. for accuracy, the uniformity in the base of the bullet is more important than the tip, so the decision is essentially to wrap the copper around the bottom and then use a die to squeeze it together at the top, which still leaves a slight open spot. i.e. the open tip is not designed to expand.
just personal opinion, but i think those rounds have a reputation for effective killing not because of some magic expansion, but because they are a rifle round and because people hit their targets more often with them because the people that use them tend to practice more and are more accurate shooters