standard trap shot is around 3% high antimony reaches 6% there may be some that claim higher but the more antimony there is the less lead is in a given pellet so it weighs less and doesn't retain as much energy at long range (it is only a small difference but it is a difference) there is also a school of thought that hard pellets resist deformation on impact with game so they don't transmit there energy as well as a softer pellet
for mine I'm happy to have 3% in hunting loads 5% seems quite OK for clays
have you thought about getting some plated? that way you will know what you are getting
