Originally Posted By: SmokelessOriginally Posted By: CatShooterThe first firing in a new chamber is the most critical moment in a cases life. That firing will determine the life of the case.
When a case is fired in a new chamber for the first time, it is a loose fit, and the primer forces it forward and slams it into the chamber's shoulder. At this first firing, there can be as much as 20 thou or more of head space, regardless of what SAAMI says.
When the case is slammed forward, there are two possible outcomes:
1 - when the pressure builds, the case walls expand and grab the chamber walls... then the pressure continues to climb, and the thin section of the case, just in front of the head (called the web) can't hold the pressure anymore, so it stretches - the body is firmly stuck to the chamber walls, and the case head goes back and hits the bolt face. Now we have a case with a thin section just in front of the head - a very badd thing. Now the case is weakened and will never be a good case, even though it may take 4 or 5 firings to fail - it WILL fail, it cannot be fixed.
or
2 - when the pressure builds, the case walls expand and cannot grab the chamber walls.
And, because the chamber and case cannot get a grip on each other, the whole case immediately slides back to the bolt face, and contains the pressure - it does not stretch, and so there is no thin section in front of the web, and it is a strong case forever (or until you screw it up).
How do extractors play a roll here? Or do they?
Push feed vs. controlled round feed.
It seems that the extractor would hold the base of the case to the bolt face [some what]. The controlled round feed especially.???
No!... The extractor can't hold the case against the bolt face.
Take your bolt out, and take a case and hook it under the extractor - now wobble it around and you will see there is HUGE play.
The primer is like a "Ram-set" cartridge - when it goes off, it really slams the case forwards - Richard Diaz, head of the Remington Research Labs, told me that the primer force is about 700 pounds (NOT pounds per square inch, but real pounds)... it makes sense to me, as I have a stainless steel pot with a deep dent in the bottom - a primed case went off in it (don't ask
) and the case stuck in the ceiling and the primer made a large dent in the pot.
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