Powder Burning Rates

Powder Burning Rates and Nomenclature

In preparing this edition of the Sierra Reloading Manual, we encountered some confusion relating to the identity or nomenclature of certain powders. This is due in large part to the fact that there has never been any standardization of the abbreviations used by different manuals to identify a given powder. As an example, Reloder 7, a medium-fast burning rifle powder manufactured by Hercules (now Alliant Powder) is identified in Sierra’s loading tables as “RE-7.” In other publications, it has been listed as Re7, RL-7 and RX7. With such similar powder names or designations as Hodgdon’s HS-7 and Accurate Arms’ No.7, the stage has been set for a potentially dangerous situation. In this particular example, the three powders listed (RE-7, HS-7, and AA No.7) are all distinctly different and are not interchangeable. Because of the lack of uniformity between the various publications, we felt that some form of index or legend would prove to be beneficial.

We also now have a situation wherein powders having the “same” numerical designation are available from several different sources. Probably the best example of this is the slow-burning single-based rifle propellant known as 4350. Available now as the original IMR 4350, Hodgdon’s H4350 and Accurate Arms’ 4350, the potential for confusion is obvious. Other powders sharing this same situation are 4227, 4198, 4895, and 4831. Each of these powders is available from both the Hodgdon and IMR powder companies. Most of these are interchangeable with the similarly designated powder, i.e. H4895 with IMR 4895, but this is not always the case. The two 4831s, for example, are quite different and cannot be safely interchanged. For this reason, we recommend that loads be used exactly as they are shown in the manuals with no substitutions. If you have any doubt as to which powder is meant by a particular designation, please call our toll-free technical service line at (800) 223-8799.

The following powders are listed by their approximate burning rate, from “fastest” to “slowest.” It must be clearly understood that burning rates are not linear. There may be several powders which have very nearly the “same” relative quickness listed together, with the next listed powder being significantly different. It should also be understood that the burning rate of any given powder can vary substantially when different cartridges are being compared. Smokeless propellants are organic compounds, and are subject to lot-to-lot variations that are unavoidable during the manufacturing process. As a result, it is quite possible for a “fast” lot of a “slower” burning powder to appear to be somewhat “faster” than a “slow” lot of what would normally be thought of as a faster burning propellant. This situation, in effect, would cause these two powders to switch positions in the following chart. Bear in mind then, that these listings are subject to change depending on the particular lots of powder involved and a host of other variables that become part of the equation. In the following chart, the column on the left lists the powder manufacturer along with their full designation for the powder in question. The center column is the designation used by Sierra in the loading tables of this manual. The right column, where applicable, are some of the designations of this powder as listed in other publications. This is by no means a complete list, and reflects only those powders used in this manual.

(Universal Clays should not be confused with Hodgdon’s Clays, or International Clays. These three powders are different and should not be interchanged.)

*(In manuals or writings published before 1973, any mention of 4831 will refer to Hodgdon’s H4831. In older manuals, it was customary to list the powder simply as A4831” with no designation connecting it to the Hodgdon line. The reason for this is simple; prior to DuPont’s introduction of IMR 4831 in 1972, the surplus 4831 sold by Hodgdon was the only powder to carry this designation. Despite their similar nomenclature, these two powders (IMR 4831 and Hodgdon 4831) are not interchangeable and must not be confused. IMR 4831 is significantly faster burning than H4831, and may produce dangerous pressures if used with data developed for the latter.)