I have to disagree with the others.My CZ 527 .223 shot well right out of the box even with low cost ammo.This was back during the Obama scare and primers were very hard to come by.Otherwise I would have just bought brass/primers right off.With any gun regardless of age you should take care not to overheat the barrel.As far as what you should try that depends on the twist rate.Faster twist-heavier bullets will shoot better.