Why do different manuals have different data?

Several factors contribute to variations in data. The hardness of different bullets affect how they obdurate to the bore which affects the drag. Different barrels can produce different results, test barrel vs. production barrel. Different lots of powder may produce variations, and different pressure measuring techniques may produce different results. All reloading data is a guide not an absolute and the reason it is recommended to start low and work up.

Welcome to
You must be 18 years of age or older to enter due to the nature of the products offered.

Are you at least 18 years old?