I understand it just fine...look at it this way, if the shooter restages the gun on the table, it bounces around a little, never stops moving, and slides off the table and hits the ground, never breaking the 170, the shooter lost control of the gun, and earns a SDQ, i.e...it came to rest somewhere other than intended. This is a dropped gun. In the same scenario, the shooter restages the gun, it bounces around a little but stops, and for whatever reason later in the stage slides off the table never breaking the 170, this is a gun falling off of a prop, shooter earns a minor safety, it doesn't necessarily mean its a prop failure just because it fell off the table. If it breaks the 170 in the this scenario, shooter earns a SDQ. The only way for a shooter to get a reshoot is if it was called a prop failure, meaning one leg of the table might have broken or some other part of the stage caused it to fall. In the original post it sounds like it was restaged a little rough and fell off the table, hence the DQ for the dropped gun.