A good rule of thumb is 1 caliber into the neck. You just can not go wrong with it. IMHO - If you are loading for hunting where you will only get 1 or 2 shots you use different criteria than you do for paper or varmints. For hunting or home defense (some thing real important) you need to make sure it is going to be as reliable as possible. To me this means that the bullet is short of the rifling leads and it functions through your magazine well. I also needs to be rugged - meaning there is no way a bullet is going to pull out of the case under recoil and it can withstand rough handling. The case must be run through the magazine and into the chamber to make sure it is going to fit nicely into the chamber. Some times you can get by with a neck size, but more than likely you will want to full length size your case every time, to make sure it will cycle. With a varmint round, I feel you can get by with a little different criteria - The bullet can touch the lands, the bullet only needs to to be into the neck enough to be held firm enough so it does not fall out or get tipped easily causing bullet run out. If you have a magazine fed gun, it still must fit in the mag unless you single load. A 30-06 has a longer neck that a 243 or 308. So saying seating the bullet base to the base of the neck does not really apply. It depends on neck length, bullet used, intended use and what fits your rifle well. I have loaded bullets with less than a bullet diameter into the case and it shoots fine, but I was not using it for home defense and not for hunting any thing bigger than a coyote. A .224 40 grain Hornady V Max only has about .200" bearing surface to start with so you can put it any where in the neck, but you are still going to get less than 1 caliber actually bearing on the neck. The 40 V max can shoot very well if your rifle likes them. Good Luck and Good Shooting