Many shooters believe that if they just use the most expensive ammunition, then they will have the best accuracy. Unfortunately, the world of shooting isn't that easy. First of all, one most understand the difference between the different kind of ammunition from each manufacturer. Take the example of Eley Tenex and Eley Tenex Gold.
Most shooters are willing to pay the premium to get the Gold version.
The way Eley decides if a lot is supposed to be sold as Tenex or Tenex Gold is by measuring the groups when shooting the ammunition in their test rifles. So if the average diameter for a 10-shot group is less than x inches then it will be sold as Tenex Gold, while a larger group results in normal Tenex. There are so many variables that affect the accuracy - lead, powder, size of bullet, the barrel, the action etc. So what is a good ammunition in one rifle can be a bad ammunition in another rifle. So one case of Tenex can have superior groups compared to a case of Tenex Gold.