Sunday, October 27, 2013

Reloading basics: The Process

When a cartridge is fired in a weapon, things happen to it.  The point of reloading the cartridge is to undo, or reverse, what happened to it when it was fired.  The best path to understanding the reloading process is a clear picture of how the cartridge itself works.

The firearm will, if all goes according to plan, send a firing pin crashing into the back of the cartridge, giving the primer a pointed blow and setting off the explosive compound inside it.  This begins the chain of events which hopefully result in a ‘bang’, and a projectile leaving the barrel to arrive someplace near where the weapon was pointed when it was fired.

The explosion and flame from the primer being struck should move through the flash hole drilled or stamped in the base of the case, in the center of the primer pocket.  This hole is there to allow the flame access to the propellant in the case.  With luck, the powder ignites and begins to burn.  It’s not supposed to ‘explode’, but rather burn very quickly indeed, in a highly controlled manner.  As the powder burns, it creates a large volume of gas, which does the actual job of pushing the bullet down the barrel and out the muzzle.  We’ll be coming back to the idea of ‘powder burn rates’.  It’s quite important and deserves some attention.
The rapidly expanding gas and flame front press the case against the chamber wall of the firearm, sealing it against gas leakage for the fraction of a second when it’s oh so necessary. This expansion also serves to help release the bullet from the case, be it straight walled or necked down.

With the fire well under way, the pressure rising fast, and the case expanding in the chamber, the bullet is pushed from the case and begins its journey.  First it must overcome whatever crimp was put in place, whether roll, taper, or collet, and then it makes the jump towards the rifling in the barrel.  In most firearms, there will be a short unrifled section of chamber or barrel before the bullet engages the rifling. This called the ‘leade’ or ‘throat’, and it’s an important feature of this process.   
(Entire volumes have been written about the process of firing a gun, and what happens within the weapon at that time.  It’s called ‘Interior ballistics’, and is critical in firearm design.  To the average reloader though, just understanding the basics is enough to get the job done safely.  There are some details that can be vastly important, and we’ll cover what we can in this limited fashion.)

Described above we have the basic sequence of a cartridge being fired.  As we’ll learn through the process of reloading the cartridge, much of what we do is simply a matter of reversing the firing sequence and returned the cartridge to the same condition it was before going bang.

Whether we are talking about rifle or pistol cartridges, straight wall or necked, there are some things that must be done in reloading the cartridge. All handloading shares these basics, with devilish details branching off to the world of precision and specialty loading.

To begin the process, the expended primer must be removed from the case.  Also, the brass case needs a good squeezing to force it from its expanded state back to its pre-fired size.  Both operations are typically done at the same time, with the case (usually lubricated first) being forced into a sizing/decapping die mounted in a press.  It’s possible to break this into two separate operations, and at times there are excellent reasons to do so.  We'll discuss this another time.

The case being resized and decapped (spent primer punched out), many handloaders would now choose to clean their cases in some fashion.  Most will use a vibratory polisher with some form of media in it; typically crushed corn cob and walnut shells.  Others will use a liquid cleaning compound.  It’s a personal choice for each reloader when and how to clean their cases, if they do at all.  While it’s not strictly necessary to clean the cases, there are good reasons for doing so.  Besides… shiny brass is beautiful!  Again, more later.

Brass cartridge cases do this expansion thing every time they are fired. Usually, the brass will also flow forward a smidgeon as well.  After a certain number of firings, the case will have enough brass migrated forward to cause an issue, both in accuracy and in safety.  For this reason, case length should be monitored and corrected when necessary.  This is done by simple measurement with either a gauge, or a caliper.  Dedicated handloaders may be seen applying micrometers to the case in the quest for extreme accuracy, where a case length difference of only a few thousandths of an inch can matter. 

For most handloaders, simply keeping their cases within a safe length will suffice.  When necessary, the cases must be trimmed a little, and then chamfered (slight reaming of the neck inside and out).  There are myriad ways to do this, from cheap and laborious all the way up to motorized, easy, and expensive.

The cartridge case being re-sized, decapped, cleaned, and trimmed if necessary; it’s now ready to reload.   Yes…. If we are doing precision rifle reloading there are still a number of things left worth doing, but here we are speaking of the basic process.

The next steps, done in order, are shared amongst all metallic cartridges to be reloaded, and the end product is a usable piece of ammo…
       *   Prime the case by pressing in a new primer.  There are several ways to do this, which will be discussed later.
       * Charge the case with the desired safe powder charge, whether by measure or by hand.
 *  Seat the bullet using a seating die, taking care to get the cartridge overall length within required bounds.
      * Crimp the case onto the bullet, if that step is being performed on this type of ammunition.
  * Visually inspect the round to be certain it is correct in all fashions.
Each one of these steps has any number of variations, tricks, and methods used by handloaders.  In some cases they will be done entirely by a machine… the progressive press… after it is set up by the reloader.  In others, the person running the bench will take great care in every step, doing each by hand with extreme attention to detail in the search for astounding accuracy. Yet, no matter the desired result, these are the basic steps to be kept in mind.


jimmie said...

Welcome back

James Clark said...

Welcome back! You have been missed.

hans said...

Great to hear from you again!

Anonymous said...

Welcome back. I am just starting to get into reloading and appreciate your insight and detailed blogs. Thank you for taking the time to share.