Author Topic: Understanding Pressure  (Read 606 times)

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Understanding Pressure
« on: November 27, 2018, 03:57:57 PM »
Primal Rights by Greg Dykstra Jul 19, 2016

Reading pressure is a required skill that all shooters must have. 

Whether you are shooting factory ammunition or your own handloads, you absolutely must be able to detect and interpret pressure signs on your fired brass.  Rifles can encounter pressure problems for a wide number of reasons.  Excessive fouling, extremely hot environmental conditions, uniformity problems with components, lubrication finding its way into your chamber, or even a surprise rain storm can all lead to a condition which will produce unsafe pressures.  When these pressure spikes occur, severe damage to your firearm may result.  This can lead to serious injury or even be fatal.  As a responsible shooter you must understand the conditions that can cause unsafe pressure.  If you understand some of the most common causes, then you will be better equipped to avoid them before they become dangerous to you or others around you.  In this article we will discuss the causes of pressure, as well as how to read that pressure on our fired brass.  We will go into detail on what those pressure signs look like with some high resolution photo's that spare no bandwidth!

First, we will talk about the role of brass during a firing event. 
The primary roles of the brass are to hold the components of a cartridge together and to contain the pressure inside the chamber for release out the muzzle.  Without brass, it would not be possible to contain the force of the small explosion inside the action of the rifle.  The two components that are most important to keeping this pressure from bleeding back into the chamber are the brass, and the primer.  The brass casings used in firearms can be thought of as a balloon.  When the powder is ignited by the primer, the burning powder expends gas which in turn creates the pressure required to launch the bullet through the bore.  That pressure causes the brass to expand to the dimensions of the chamber and essentially "plug" the rear of the chamber, giving only one way for the pressure to escape; out the muzzle.  The primer has a role in this as well, due to the fact our cartridges must have an ignition source, and this is accomplished via the flash hole inside the primer pocket of the brass.  This means that pressure inside the brass is also transferred through the flash hole onto the primer cup.  Thus, signs of excess pressure can be seen on both the brass and the primer.  Obviously the complexities of interior ballistics go far beyond the scope of this article.  Suffice it to say that there are entire libraries of books which one can read to better understand what is happening in a rifle chamber.  One such book is Interior Ballistics; How a Gun Converts Chemical Energy into Projectile Motion, by E.D. Lowry.  For the purposes of this article, it is sufficient to say that the brass and primer keep the pressure contained inside the chamber, rather than bleeding out past the bolt nose and through the bolt itself. 


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