What causes hangfires?

[essayons21]

Today I was shooting Korean M2 ball with a 1975 headstamp out a Remington 700 in 30-06. It was a box that has been riding in my range bag for probably 2 years or more.

The very last round I squeezed the trigger and heard the pop of the primer then there was what seemed to be 1/4 to 1/2 second delay before the bang. The round actually hit the same hole as the previous shot, which surprised me.

It was the first hangfire I have experienced in many tens of thousands of rounds fired, and I was curious as to the possible causes.

 

[Slamfire]

Ammunition deteriorates with age.

Double based powders start deteriorating the day they leave the factory. Nitroglycerine and nitrocellulose want to combine to form a lower energy compound. Nitric acid gas is released as a by product of this reaction.

The reaction rate is directly proportional to heat. The hotter things are, the faster the migration and reactions.

The Army scraps ammunition based on clock time. 20 years for double based powders, 45 years for single base.

For more information:
http://www.almc.army.mil/alog/issues/JulAug08/propellant_stab_eq.html

Anyway, with ammunition as old as yours, well expect some funnies. You have no idea where it was stored, how it was made, and how the powder is doing.

 

[Grumulkin]

Hang fires are caused by light loads. When a powder deteriorates, it essentially becomes a light load.

It's well known that starting a bullet that is jammed against the lands takes more pressure than starting one with a little jump to the lands. So, if you start a bullet off with too light a load, it can hit the barrel and hesitate a bit. All this is of course happening in a very short time span. As the bullet hesitates, a lot more pressure is needed to get it started down the bore again. The powder continuing and the resultant gas with no place to go eventually supplies the needed pressure which is a lot more than usual.

The bullet hesitating is what we see as the hang fire. The rising pressure in some cases causes a bolt thats frozen tight, a cracked stock or other signs of extreme pressure.