How to analyze your brass for signs of Overpressure

Some people say that you should only reload brass certain number of times before you should throw away. While no one wants to blow up their gun with a bad cartridge it is up to each individual to work within safety contraints they are comfortable with. A more rational and economical method exists, IMHO: Inspect each piece of brass around the second use and discard them once you start sending text signs of overpressure. You also should closely inspect spent cases when testing a new load recipe- regardless of whether or not you saw it published somewhere.

Pro tip: Heavily scrutinize R-P brass stamped with “AAC 300 Blackout”. It is the thinnest brass I have ever seen- as in .22 thin. After 3-4 tours of the supersonic circle of life (they were factory cartridges) I am seeing some wear on some of them- imprints and case head separations. While having your bolt stick or seem 'heavy' is a strong indicator that something is wrong with the ammo there are some subtle (and not so subtle) things you can watch for that indicate overpressure…

A progression of flattened primers under increasing pressures

  • Flattened primers
  • This is commonly cited as the thing to look for but it is not an absolute. Some primers will flatten at safe pressures, some won't flatten at all and some primers can even blow out of the cartridge. Definitely check for additional indicators if you see this though- I view oddball primers as the clue that closer investigation is required.
  • Ejector imprints
  • These are another sign that merits closer investigation. Note how the case on the right shows that dark ring- this is also an ejector imprint. While there are some reasons that you may get these without overpressure being involved the way I see it is that 2 possible indicators deserve a close look at the case and double-checking the cartridges.

  • Greatly enlarged primer pockets :
  • Easily identifed by misshaped primers- during ignition the primer flows into the new bloblike shape of the primer pocket. You can also see dark rings around the primer- an indication that the primer pocket is no longer sealing off ignition (read: throw that case away). Note that you may not always see such dramatic rings like the ones above

If you see any of the three overpressure signs listed above you can test the primer pocket:

  • Decap suspect brass and try to press the case head over a primer by hand. If the primer doesn't hang up a little the case is no longer safe to use.

Dangerous and Certain Signs of Overpressure or Excessive Case Wear

If you encounter anything that resembles the two indicators listed below JUST DISCARD THE CASE. Also double check you load data and for your own safety pull the bullets and recycle your components from that batch of ammo. It can be really frustrating but safety and precaution should be guiding principles when reloading.

  • Case Head Separations
  • When the case fires the head of the cartridge wears and reloading dies cannot replace that material. The case stretches too- if you are trimming your rifle cases excessively start watching for lines like the ones above on your cases. Even if you are not yet trimming the brass don't reuse cases like this because you surely do not want the head to shear off during ignition.
  • Case Ruptures
  • Case ruptures are a definite warning sign. If you see anything like the cases above while testing a handload or any other ammo please stop firing it immediately. Follow up by disassembling any remaining loads from that batch and back your load recipe down a grain.

For a handy review or future reference this video has great examples and explanations:


1 thought on “How to analyze your brass for signs of Overpressure

  1. Pingback: Making Hard-To-Find Calibers From Common Ones | Loves Old Stuff

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