Air space, how much is a concern?

[CZ_Brno]

As a rule of thumb what percentage of the case should be filled with powder before you start getting concerned with hang-fires or a dangerous detonation from the primer igniting the powder across the top all at once when it's laying horizontally across the bottom length of the case?

And what's a good filler to use? I heard that dryer fluff works well.

 

[KODIAK BEAR]

To be safe and consistent, do not use less than the minimum powder charge, nor more than the maximum charge as established from a reliable loading manual. I often use light charges, but never lower that minimum, and have never experienced a problem
In the past, when I used a filler for light 9mm and 38 loads, I used Dacron, which is obtainable from any quilting or fabric store.

 

[Craig67]

CZ Brno,

You want to be very, very careful using reduced loads of slow burning powders.

Richard Lee devotes a half chapter or so to reduced loads in "Modern Reloading". I would highly suggest getting this book as a start and then following that up with some research on dedicated reloading sites.

Going below minimum is almost as scary as going above maximum loads.

Craig

 

[John Y Cannuck]

The big danger is that of double charging when using small amounts of slow powders in big cases.
But there is evidence of "detonation" very un-proven, but.....

Some very experienced reloaders have claimed detonation destroyed their guns. Others argue that they must have double charged.
As I understand it, the detonation idea has never been proven in a test barrel.
Check your loads very carefully.

One guy a few years back advanced the theory that the powder was "flashing over" causing the bullet to move forward into the lands, at which time the superheated main charge detonated.
All theory, you will have to develop your own beliefs.

 

[H4831]

John, you sure have got it right.
Double charging with a powder that is less than half a case full at full pressure, is a very real danger and probably the most common cause of severe gun damage.
However, to admit putting in a double charge is admitting to making a mistake and handloaders don't make mistakes.
It is so much easier to blame it on something else. The primer flashed, the bullet moved/the bullet stuck, the pressure went up blah blah blah.
What an absolute load of Bull Shoot!