[Jeff Higgins]

There are only four primer sizes available; large rifle and small rifle, large pistol and small pistol. The size used is dictated by the case into which it will be seated. Generally speaking, .30-'06 and belted magnum case head sizes take large rifle primers, and the .223 / 5.56mm case head sizes take small rifle. With handguns, generally speaking anything .38 caliber and smaller take small pistol; .40 and up take large pistol.

The primer pockets on each of these four general groupings are all different sizes, even though large rifle and large pistol look about the same, as do small rifle and small pistol. They are not. Rifle primer pockets are about .0005" to .001" bigger in diameter, and just a touch deeper than pistol case primer pockets. Pistol primers are, therefor, too loose to be safe in rifle cases. Don't mix them up.

Each of these four sizes are further divided into "standard" and "magnum". This has nothing to do with whether they are used in standard or magnum calibers, believe it or not, nor the physical size of the primer, but rather indicates how much priming compound it contains, along with how "hot" it burns. In very broad terms, standard primers are for lighting light to medium charges of fast to medium burning powders, and magnum primers are for lighting bigger charges of slower burning powders. This is the only aspect of all of this that can get confusing - it is common practice to use standard primers in magnum cases with some powders and some bullets, and an equally common practice to use magnum primers in standard cases with some powders and some bullets.

That is where recognized sources of reloading data come in - they will all list the primer used in a specific combination. Changing primers in a given load can and will change pressure and velocity developed by that load. Not necessarily just changing from a standard to a magnum primer, but also when changing brands of primers, even if both brands are the "same" as far as standard or magnum. In other words, changing from a standard CCI primer in a given load to a standard Federal primer in the same load will result in different pressure and velocity. This isn't a bad thing, but rather something to be aware of, and also a pretty good way to get that last little bit of refinement out of a given load.

Speer has what is probably the best manual available for basic reloading information such as this. It has several chapters explaining everything you will ever need to know about primers, cases, powders, bullets - the works. The Lyman manual is excellent for this as well. Both offer far more than simple lists of loads for various calibers; they are very good tutorials on the hobby of reloading in general. Some other manuals supply comprehensive tables of loads for every caliber on earth, but are lacking in the nuts and bolts instructions on how to use the equipment to assemble the loads, or why certain primers are used with certain powders in certain applications, and that kind of "in depth" information. The Speer and Lyman manuals all cover this stuff in great detail.