August 17, 2022
A rifle cartridge is made up of only four components—two energetic and two benign. The energetic ones are the primer and the propellant. The case and the bullet are only benign until the firing pin strikes the primer. At that point, they both obturate almost instantaneously. The case seals the chamber to ensure the extremely hot primer and propellant gases exit the muzzle and don’t flow back through the action into the shooter’s face. The bullet jumps forward and is engraved into the spiral rifling, sealing the hot gases behind it as it accelerates down the bore. If all goes according to plan, the spinning bullet exits at the desired velocity on the way to the intended target, and the expended cartridge case and rifle are still intact. Hopefully, you’ve only suffered a non-injuring jolt from the recoil.
A cautious and competent handloader always develops a plan before starting to assemble ammo. The most important feature of the plan should be answering the question, “What will these handloads be used for?” After you’ve selected a cartridge suitable for the specific purpose (i.e., plinking, hunting, or competition), the next step is to round up the appropriate components required to fulfill your objective.
There are usually several brands of a specific cartridge case to choose from. Although they share essentially identical external dimensions, they almost assuredly differ as to material constituents, metallurgy, and internal dimensions. The number and types of bullets and smokeless propellants available (usually) is almost mind-boggling. Once you’ve selected the cartridge you plan to load, the choices and combinations can be winnowed down, but you will likely have a broad selection to choose from. Often the choice is based purely on something you’ve read in a magazine, seen in a video or on television, or a friend’s recommendation.
Primers are less of a challenge. Large and small primers are available for either “standard” or “magnum” rifle cartridges. Most small-capacity cases use Small Rifle primers and larger-capacity rounds use Large Rifle primers. A few are also offered with either large or small primer pockets.
Typically, more energetic “magnum” primers are used only when loading spherical propellants (especially if the rounds will be fired in cold temperatures) or if the charge weight exceeds approximately 60 grains. The charge weight threshold is an empirical conclusion categorizing standard and magnum cartridges regardless of their actual nomenclature.
Let’s say you’ve decided to handload a batch of .30-06 ammo for hunting mule deer this fall. The next step is to pick a suitable bullet. I prepared an extensive load development experiment years ago using a popular 180-grain conventional cup-and-core bullet. Federal and Alliant provided all of the other components and conducted a parallel development effort. We arrived at the exact same powder charge independently. Federal based their stopping point upon reaching an established pressure level. My decision was solely based on velocity and accuracy results.
As a follow-up, we embarked on an even more extensive project. I acquired 19 additional 180-grain bullets of different brands and/or construction. Federal provided 20 boxes of calibrated .30-06 cases, and I loaded each box of 20 rounds with the same propellant charge and primer I’d developed earlier before simply substituting bullets. All were seated so the multiple configurations fit the calibrated cartridge gauge Federal also provided.
The peak chamber pressure of the original .30-06 test load measured 57,000 psi. However, the recorded pressure levels of the additional test loads varied from about 52,000 to 61,500 psi. Same lot of new brass, primers, propellant (the same charge weight), and the same bullet weight. It was an eye-opening experience and demonstrated how important it is to carefully research reliable load data sources that provide full descriptions of the components used to establish the load recipes listed. Many mainstream load manuals also provide the corresponding pressure data.
Just recently I compared the performance of several rifle cartridges charged with similarly labeled Hodgdon, IMR, and Accurate 4064 and 4350 propellants for the upcoming 2022 edition of the Hodgdon Annual Manual. I chose to use Winchester Large Rifle (WLR) primers in five standard cartridges and Federal Large Rifle Magnum primers in one round tested.
One of the cartridges was the classic 8mm Mauser. While I was preparing a final batch of test loads, I noticed that Hodgdon listed the Remington 9½ Large Rifle primer instead of the WLR primer. I wondered how much difference using the primer would make, so I prepared another batch of five rounds each capped with CCI 200, Federal 215 (magnum), and Remington 9½ in addition to those with WLR primers. They were assembled in PPU brass, charged with 45.1 grains of IMR 4166, and topped with Hornady 195-grain JSP bullets seated to a cartridge overall length of 3.0 inches.
The results are listed in the accompanying chart, and as you can see, the average velocities ranged from 2,448 fps to 2,517 fps (a difference of 69 fps), depending on which primer was used. My point is little differences cannot be ignored when you’re loading ammo. They can and often do impact how your handloads perform.