I use the lee factory crimp die. Johnnies reloading bench did a test with some Bobb's bulk bullets in 223 and found no differences in accuracy. . I have found with match bullets and thinner jacketed bullets without cannelures you need to go easy or you can have problems. I generally use a light crimp over all and it seems not to cause any accuracy issues that I can tell, but I am not competition shooter. I did just shoot a 0.85 moa group at 100yds with 6mm arc with a light crimp.