If I put 1/2 gr Bullseye in a 45/70 and a .454" lead ball over wads.....

a) Seated in the case mouth, the fired ball bounces off wood.

b) Seated deep in the case to compress the powder, the fired ball penetrates an inch of wood.

Both loads make the same pellet gun like sound from the muzzle, but the seconds load makes a much louder sound when it hits the wood.

The difference between the two loadings can be though of as expansion ratio.

Every time a gas doubles in volume, the pressure drops in half.

The second load starts with a much higher pressure, but both loads result in the same muzzle pressure ~ 1 atmosphere above ambient... the threshold of supersonic gas escapement.

[Linked Image]
Here you see Hawk has defined expansion ratio as = expanded / compressed.

http://en.wikipedia.org/wiki/Expansion_ratio
Here you see the chemists have defined expansion ratio as = compressed / expanded


http://hyperphysics.phy-astr.gsu.edu/Hbase/thermo/diesel.html
In diesel engines, expansion ratio is = expanded / compressed


http://www.frfrogspad.com/intballi.htm
Here you can see expansion ratio = powder fill ratio
Maybe they made a mistake.