June 29th, 2007

Detecting Excessive Pressure in Cases

With the relentless pursuit of more velocity and the “next higher node” by many reloaders, it is important to pause and think about safety. And one has to remember that most brass will not hold up to high pressure the way Lapua or RWS does. Many readers have asked us–“How does one detect excess pressures.” Well first, one can obviously monitor the primer pockets and measure the diameter of the case near the web–excessive stretch or pocket loosening is a sure sign you’re running too hot. There are also many visual signs of over-pressure which you can see. Reader ScottyS provided this comparison photo of cases, showing the tell-tale signs of over-pressure.

rifle cartridge brass pressure signs

Scotty tells us: “These samples were from a lot of Federal soft-point hunting ammunition that were fired in a custom .308 with a chamber on the tight side (although still allowing a .308 Winchester ‘GO’ gauge). Among the pressure symptoms were heavy recoil, sticky bolt lift, and the left case had to be manually removed from the boltface. This demonstrates why: 1) you should never assume that all lots of factory ammo are the same (and safe); and 2) you should ALWAYS wear eye protection. This also shows how high pressure can spike once you approach maximum load levels.” Scotty noted that there was a big pressure difference between the left case and the right case, although both were from the same lot of ammo. So take heed–always take precautions when testing new ammo, even if it is factory-loaded.

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