I have to agree that not all load books are created equal. I would suggest the Hornady load books for beginners. The beginning of their books is full of information and explanations of what is going on in the chamber when a shooter pulls the trigger. There are warnings posted in the load pages about hot loads in certain rifle designs as opposed to what they used for a test rifle. There are warnings about using different bullet designs. (The original post was about mixing brass, not bullets.) I have made quite a few reamers in my time and the case body tolerance (SAAMI) is usually around .002. The ammo makers specs for the case body diameter is usually around .008. Add the headspace allowance to that and it really is pretty much. Other than the neck being too thick for the chamber that was cut, mixing good brass means nothing. "Good" meaning brass that was not fired 5 times already. I usually buy new brass, but still check every case before loading. I often find flaws in new brass. Years back I took .303 British brass and re-worked it into 6.5 Japanese brass. I cut one case each the long way and the .303 brass had a thicker wall down by the bottom. I did not see one bit of difference at the range with the same load. Anyway, what gave the "Newbee" the idea to shoot hot loads? I NEVER saw a load book that condoned shooting hot loads for accuracy. I bet he read it on an internet forum.