Brass can and does wear out.  My latest recipe suggests that about 10 reloads 
is the limit.  Some have been reused seven times with this recipe.  Some 
recipes are only good for two or three.  At failure, the brass will crack but 
the bullet behavior will be normal.  It can then never be reloaded.

The most critical aspect of reloading is powder charge.  There are hundreds of 
different types of powder with different burning rates and gas volume 
produced.  Different bullet weights require different powder charges.  Too low 
a powder charge may fail to cycle the action of a semi-automatic.  A very low 
charge can drive the bullet half way down the barrel.  The following round is 
exciting if the barrel has not been cleared.

Too high a powder charge can strip lead or copper from the bullet and foul the 
riflings in the barrel.  As an extreme case it can cause the cylinder or 
chamber to explode.  Extremely energetic powders are used only in small 
amounts.  The cartridge case may be able to hold several such charges without 
overflowing.  Some cases can even hold triple charges.  

The most dangerous time of reloading is powder charging.  A phone call or 
other distraction can cause you to skip a cartridge or double charge one when 
you return to business.  I generally weigh the first, middle, and last 
charges; as well as visually confirm that all 50 powder levels are the same.  
Purist bench shooters weigh each charge, but these folks are extremists.

There are reports that the primer alone can drive a bullet halfway down the 
barrel.  If that happens, the next one is exciting.  I have used a primer 
without powder on the 44 but have never been able to get it to move the 
bullet.  It never even makes a sound when the primer goes off, other that 
normal sound of the hammer impact.

I had one go halfway down the barrel on a Texas ranch 20 years ago while fan 
firing.  I was shaking badly when I eased the hammer down on a life round.  
Although I found a rod and hammered it out, I never found out why it 
happened.  It was likely a half charge.  It takes about one fourth charge on 
mine to drive the bullet halfway down the barrel.

I have fired some 357 rounds that I loaded 10 years before with no problems.  
Non-corrosive primers have been in use for over forty years. I think that 
modern ammo should be good for fifty years if kept dry to prevent corrosion.  
The literature says that old ammunition is slightly faster burning and results 
in slightly faster muzzle velocity.  I am not qualified to judge this matter.