It can be chasing ones tail. Rim thickness is one method, supposedly for even headspace. The object is to minimize flyers out of a group. The group may or may not be good, just no obvious flyers. I have always gone with match ammo that the particular rifle likes best. More money.. The groups however speak for themselves. Some times cheap ammo shoots very well, only the rifle knows. Then one can get into different lots of the same ammo.. Which of course is very hard to buy again.. It can be a large dark hole one falls into.
