When are pressures too high?

Commercial load data defines the boundaries most of us reloaders need to observe. This important safety practice costs very little in terms of real performance in the field. Use your favorite ballistics calculator to estimate the drop for the starting load (typically 5-10% below max) and the maximum load at 300 yards. Then compare that to the holdover, if any, you might need to get the bullet inside the canonical 10” vital zone. The bottom line is that even though the starting load drops a bit more, it won’t normally make a big difference in your sight picture at customary hunting ranges. Similarly, the bullet’s lethality is very close to the same at both the starting and the maximum loads.

The discussion is divided into four parts. The first part introduces the discussion and gives a basic procedure for using cartridge case head expansion. The second part is a thumbnail sketch of methods used by commercial houses to assure compliance with SAAMI standards. The third part is a more comprehensive method for using case head expansion to detect when pressures are getting too high. The fourth and last part describes the results of a series of engineering calculations that suggest the method is viable.

Click on the highlights below to navigate to the sections:

• Introduction – Detecting Pressure Signs
• Pressure Testing by Commercial Manufacturers
• Judging ‘Safe Pressures’ by the Handloader
• Why Parametric Case Head Expansion Can Work

The author is deeply indebted to VarmintAl.com for giving permission to use the results of a calculation that is a rather strong example of why the method can work. He also provided significant constructive criticism along with Craig Eagle, Dick Hatfield, Greg Luli, Paul Scott and Todd Slavic for critical reviews. AmmoGuide’s tloC54 provided an excellent review of the first web version of the four notes. These reviews enabled the writing of a more readable and complete discussion.

I have certainly discussed this topic with others, and may have overlooked a name or two. If you have helped, please remind me and I’ll be happy to update this paragraph.