This is the time of year that you want to set up your reloads and select your factory shells for the coming season. Factory screw chokes often do not deliver what they claim to. Patterning is the only way to know what you really have. Antimony is the hardening agent used in lead shot. Harder pellets deform less when they are shot and so produce better patterns.
More antimony is good.
The problem is that antimony costs about five times what lead does, so the manufacturers have an incentive to cut costs and use as little as they feel they can get away with. Your ignorance is their bliss. Percentage of antimonial content is the McDonald's Secret Sauce of the reloading world. That is a big difference. The Remington Gun Club lower cost factory target loads were even worse than the Peruvian reloads at an average pellet count of 141.