Remember in this post I mention batching brass, the cases? That's done as every time a round is fired the case expands which is why it is resized in the resizing die as part of the prep process of reloading.

It lengthens too, which means it needs trimming to within manufacturers tolerance of case length. So, brass is cut off the neck to do this.

Eventually the case becomes too unstable to use. They crack. When they are fired, if that happens, it goes very badly for the operator. That's why each case is meticulously checked once cleaned and thrown away if found to lack integrity.

I have my cases annealed (after firing) to return the metal to it's original metallurgical state of hardness/malleability etc. This extends the life. I get about 5-6 reloads from each case, roughly, then they are discarded.

I can hit a torso sized target at over a mile, (I never say the true extent of my range). I have done many posts on the process and what comes into play and as you say, there are many variables and many elements.

I hope this helps.