Gentlemen; you have brought into focus the reasons why old loading data should never be used.
Elmer Keith, bless his soul, was a true pioneer, but some of his data yield dangerous overpressure. Piezoelectric pressure measurement was unknown in his day, and the bulk of data to be found in printed reloading manuals has yet to be tested in this manner. It was only a few years ago that Olin (formerly Winchester) retested their data and markedly reduced their recommended loads in several calibers.
The above link to Alliant is incorrect. The correct link, and all other links as well, are most conveniently found at this site: www.shooterslinks.com/
Click on 'categories', then 'manufacturers, non firearm' and you will find all the loading data sites at your fingertips.
Alliant's URL is: www.alliantpowder.com/
At this site, they list a maximum of 20.6 gr. of 2400 for a GC 240 LSWC. However, there are problems with this datum.
The exact bullet type is not specified. Thus, while an OAL is given, the critical measurement, how much bullet is seated into the case, is not possible to determine. Further, the case type is not given, although the primer type is. Even if all these data were supplied, you would need to use the actual case lot, bullet lot, primer lot, and powder lot to make sure you duplicated the load exactly.
Thus, the charge weight given is the MAXIMUM. You must begin at a lower charge and carefully work up your load, watching for signs of excessive pressure. To say that you are under the maximum for a given load can be true only if you have matched every component in the tested load precisely.
Each load you work up is a composite of many variables due to the differing nature of the components used. Further variables, of course, are introduced by the particular firearm in which the loads are used. Start low, and be safe.
Walt Welch, NRA Life 1972, reloader over 40 years.
[This message has been edited by Walt Welch (edited October 15, 1999).]