Causes of Case-Head Separation
On his Riflemans’ Journal blog, German Salazar has posted an excellent article about cartridge Case-Head Separation. We strongly recommend that you read this article. German examines the causes of this serious problem and he explains the ways you can inspect your brass to minimize the risk of a case-head separation. As cases get fired multiple times and then resized during reloading, the cases can stretch. Typically, there is a point in the lower section of the case where the case-walls thin out. This is your “danger zone” and you need to watch for tell-tale signs of weakening.
The photo below shows a case sectioned so that you can see where the case wall becomes thinner near the web. German scribed a little arrow into the soot inside the case pointing to the thinned area. This case hadn’t split yet, but it most likely would do so after one or two more firings.
One great tip offered by German Salazar involves using a bent paper clip to detect potential case wall problems. Slide the paper clip inside your case to check for thin spots. German explains: “This simple little tool (bent paper clip) will let you check the inside of cases before you reload them. The thin spot will be immediately apparent as you run the clip up the inside of the case. If you’re seeing a shiny line on the outside and the clip is really hitting a thin spot inside, it’s time to retire the case. If you do this every time you reload, on at least 15% of your cases, you’ll develop a good feel for what the thin spot feels like and how it gets worse as the case is reloaded more times. And if you’re loading the night before a match and feel pressured for time — don’t skip this step!”