Older manuals, the Speer #8 in particular, have powder charges listed that are higher than anything more recent. Some say it's due to the fact that there wasn't all the litigation that there is now. That is partially true, but a lot of older data was created without the use of presssure guns since they are costly pieces if equipment. It was worked up by checking for what was once considered normal signs of excess pressure. Nowdays, a lot of the old "pressure check" methods have been proven totally unreliable in labs while using a pressure gun. There are just too many variables from gun to gun, loading practice to loading practice, for the old ways of checking pressure to be very accurate. (There was an article in Handloader magazine about a lot of this, just a couple of years ago, I still have it somewhere)Also, SAAMI has lowered the maximum average pressure of a lot of rounds from what they were back then, which leads to lower listed powder charges in the newer manuals.
Some loads listed even today are not pressure tested by most labs. The 340 Weatherby comes to mind instantly. Very few labs have a pressure gun for that round, which is why its ballistics from the manuals doesn't really seem any better than that for the 338 Win. I have owned several of both (still own a 340), and can tell you that with proper loads, that were worked up in a lab pressure gun, there's as big a difference between it and the 338, as there is between the 30-06, and the 300 Weatherby/300 RUM. Quite a bit in other words.
