Is that any more complicated than precisely weighing the powder in each round? I suppose cases and bullets can vary slightly in weight as well. Are there any other factors I not thinking about?
Sorry, the easiest way to answer this is cut and paste:
"Manufacturing match grade ammunition and other parts requires extremely tight tolerances and quality control. It is not unusual for match-grade ammo and parts to cost ten times more than the comparable non "match" counter-parts, owing both to the increased labor expended in creation and much more rigorous testing. Match grade ammunition is often subjected to higher randomized testing to increase the statistical likelihood of detecting a dud round. Match grade components are often selected by testing the performance of multiple, identically configured firearms and then eliminating those that don't perform to expectation."
Tight tolerances and quality control is the goal for loading Match ammunition, consistency in the strike of the bullet on target, eliminating dud rounds or flyers.
When I was shooting matches (My Marine Corps days) we shot on targets that had (in the center) a 10X, hits on the X (also the same score of 10 for a bulls eye) were used as tie breakers. Every match I was in came down to the X count.
By having matched ammunition and a tuned weapon you can eliminate some of the variances you will encounter during a match.
Even though I no longer shoot sanctioned matches it is still a matter of pride (and sense of accomplishment) one holds for his ability when shooting with your peers or teaching ( who wants to be taught by a shooter that can't hit the center?).
A cheaper way (but not a completely fail safe way) is to buy factory matched ammo in bulk (a case at a time) and tell the store that you require the entire case to be of the same lot (lot, ammo loaded during the same loading run) not all stores will do this.
Hope this answers your question Delmar.
P.S. There are guys that during practice bring a portable reloading station to the range and make changes to their ammo, changing powder, powder loads, powder manufacturer and bullet configuration, but I don't think I will ever get that serious about it.