What are the differences, if any?

Traditionally a Sacramentary has only the priest's proper parts, whereas a Missal contained the entire Mass. Modern Sacramentaries usually have 1) the Ordinary, 2) Rubrics 3) The Collect (opening prayer), prayer over the gifts, and the Post-communion (concluding prayer) 4) the Preface and Canon

The readings, as well as the Introit (Entrance Antiphon), Gradual or responsorial psalm, Offertory antiphone, communion antiphon are not included.

In a Missal, all of these are included. Missals begin when priests began to say Masses without other sacred ministers and a choirs. Hence having all in one book was convenient. Up till the early Middle Ages you had an Antiphonary with antiphons, for the choir, a Graduale, a Sacramentary, an Ordo, an Evangelistarum (Book of Gospels), an Epistolarum (book of other biblical reading), or essentially a book for each distinct minister. Some of these still exist (such as the Graduale for the schola, or a Book of Gospels for the deacon), etc

Missal = Sacramentary + Lectionary

The Holy See has declared that the Sacramentary should be called as the Roman Missal.

Check GIRM (General Instruction to the Roman Missal):

http://www.usccb.org/liturgy/current/GIRM.pdf

ummm ... I don't see where it makes that change, anywhere specifically?

It's going to be changed this November:



Note that says "Roman Missal" instead of "Sacramentary."

From http://www.adoremus.org/CDW-ICELtrans.html

A. The word "Sacramentary", evidently chosen to distinguish this book containing the prayers of the Mass, on the one hand, from the Lectionary, on the other, seems nevertheless to have had the adverse effect of furthering a mistaken conception of this "Sacramentary" as a new and somewhat autonomous liturgical book for the English-speaking world. The term "Sacramentary" is not characterized by a linear historical development, and the present book also contains antiphons and other elements that were not in the ancient or medieval books commonly designated sacramentaries, at least in academic usage. Accordingly, the Congregation asks that from now on the book be referred to in English as The Roman Missal, and that the official use of the word Sacramentary be discontinued in reference to it.