If you are buying brass from a small~ish dealer, like Sinclair International, they will give you all the same lot number IF you ask.
I would agree with what has been said.
For small varmint rifles, like .223's, I usually get 500 pcs, just because it's easier to load them up in the winter and spend the summers shooting.
For my Prairie Dog rifles, I have 1,100 for my 6mmBR, and 6,000+ for my two .223s.
Larger varmint rounds... I have 550 for one of my 6mm Rems, and 400 for the other.
For the 264 Varmint rifle, I have 270 pcs.
For my target rifles, I usually have 300 to 400 pcs.
Large game rifles, 100 pcs is enough.
For the 50 BMG, I have 460 pounds of empty brass (I think it's somewhere around 3,600 pcs)... I got a "deal" that I couldn't refuse.
Consider your usage, and how you load. If you don't shoot much, then less brass is needed... if you spend your summers in woodchuck fields, you might want a lot of brass... or spend evenings during the week to reload.
It's really up to how much you shoot, and the way you load.
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LRH member #23