Before I get into the question I have a couple of things to ask:
1. If this isn't the right place please move the thread;
2. I want to post the description of the Boulderhead Mace.
Ultimate Equipment describes the Boulderhead Mace as:
"The head of this +1 heavy mace is made from a single piece of
roughly spherical, polished granite. Once per day, the wielder
can command the mace to release this head, which grows to
the size of a Large boulder and rolls quickly in a direction the
wielder specifies. The boulder rolls in a straight line for up to
60 feet, crushing everything in its path for 3d8+5 points of
damage (Reflex DC 19 half). The boulder collapses into rubble
and dust at the end of its path or if it encounters an obstacle
it cannot break through or roll over, creating a 10-foot-square
area of difficult terrain. A new stone mace-head grows on the
weapon’s haft over the next 24 hours, and it is unusable as a
weapon until the head regrows."
Now a medium sized mace is described above. Let us for the sake of argument presume we have a Large Boulderhead Mace. As such the mace does 2d6 worth of damage.
1. But what does it do when the head detaches?
2. Does it gain another d8 to do 4d8+5?
3. Does the Reflex save change?
4. Where does the (+5) come from?
5. Does it change if the weapon size changes?