I believe it was Handloader Magazine. It remains a timeless rescource.As you read the articles you will notice Ken Waters writing style, his loading knowledge and ability to communicate grow over the years. Many of us do not realize Ken Waters started the Pet Loads series in Shooting Times magazine about 1962. Certain articles are quite poor, the original article on the 30-30 for instance, the 30-30 follow up though, is extremely well done.
The original article on the 300 Savage is very interesting with the follow up even more so. A very thought provoking series of articles.