In the common context, explosive means it burns rapidly.
There are probably several different legal definitions of
explosive.

Anyone who want's to see the difference between smokeless
and black powder only needs to lay out a line of each and
touch each off with a match. However, the burning of
unconfined powder is quite different from compressed
powder. If you want to see dramatic differences put the
same amount of blackpowder in a rifle and compress one load
then try it without compression. Or, put it in any other
container and then watch what happens. There is a reason
that you use a ramrod with black powder even when the ball
will roll down the barrel. And if you reload cartridges,
you know that blackpowder reloads are compressed and with
smokeless powder there is often a lot of space between the
cartridge and the bullet.

The statement that antique firearms use 4F and 3F is
incorrect, pistols, small rifles, and flash pans use the
finer grains. 2F is often used for larger bore rifles.

You don't need pipes for blackpowder or smokeless powder to
go boom. Paper tubes work just fine, e.g., fire crackers.

Chris Lewis wrote:


Sorry, wrong.

_Neither_ smokeless powder (eg: pyradex) or blackpowder are explosives.

["Explosive" being defined officially as when the gas expansion is
above the speed of sound.]

The difference between gunpowder and smokeless powder is simply that
gunpowder's coefficient of combustion is such that it burns _very_
fast even if uncontained - but still not an explosive shock wave.

How fast depends on the grain size (primarily). Antique firearms
usually use FFFFg (very fine) or FFFg (fine). Antique firearms
simply don't work properly with coarser black powder.

The only way you can get blackpowder to "go boom" is contain
it inside something like a pipe with threaded on ends. Then you're
getting the boom from the pipe overpressuring and throwing bits.

Pyradex, when unconfined burns fairly slowly comparatively.

A hand full of smokeless powder
can be touched off with a match and will only burn, admittedly very
fast and you may loose some eyebrows, but a hand full of blackpowder
would take your hand off when a match touched it.

Sorry no. Blackpowder does the "flash, lose eyebrows" trick[+]. Pyradex
uncontained is _much_ tamer. More like safety matches burning.

The only way you can get firearms to work with pyradex is to contain
it to build pressure, then it burns much faster. Blackpowder burn rate
doesn't depend nearly as much on pressure.

If blackpowder was an explosive, you couldn't make rocket motors with it.
You couldn't use it in a firearm (it's a little late to find that out
now ;-)
((much deleted to save space))
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.