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Old 07-21-2007, 11:54 AM
  #4  
Prairie Wolf
Fork Horn
 
Join Date: Jan 2007
Posts: 260
Default RE: Signs of pressure?

Don't put too much trust in so called pressure signs either. When they show up you have too much pressure, but if they don't show doesn't mean you are safe.

Signs to look for:

Primers: The primer is completely flat. The primer has no radius left on the outer edge and has filed the whole primer pocket. You can also look for 'cratering' which is a raised edge around the primer dent. This is caused by the primer trying to flow back around the firing pin into the firing pin hole.

Brass flow: The bolt lifts hard. The case is being stretched back against the bolt. Brass has a little spring back, and so does the steel bolt. When you get too much pressure, the bolt flexes back and allows the brass to stretch longer. Then the bolt springs back and presses against the brass. Under normal pressure, the brass will spring back and still be smaller than your chamber, and the bolt opens easily. Under higher pressure, the steel chamber and bolt flex too and allow the brass to expand larger than the chamber, then the chamber and bolt spring back and a the friction makes the bolt lift hard. The brass will also flow, distorting the headstamp and making a shiny spot where the brass flows into the extractor groove. The bolt may actually have to shave off a part of the casehead in order to open.

I have seen several articles that state that many times you can be well over allowable pressures and never see pressure signs. So if you have signs, you are too hot. If you don't, it doesn't mean you have a bunch of room to play with over the max charge.

You also get false pressure signs that mean you have too low pressure. Black soot past the shoulder of the case means the pressure isn't high enough to stretch the case into a good seal on the shoulder.

Primers sticking out past the back of the case can mean the pressure isn't high enought to stretch the casehead back against the bolt and force it back in.
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