I thought about the 50-50 mixture because that way would be a little denser than lead,but harder than pure lead..
                        DENSITY    MELTING POINT   MOHS HARDNESS
COPPER            8.94g\cm3      1084 C                      3.0

LEAD                11.34g\cm3      327 C                      1.5

So the 50:50 alloy would be about 10g\cm3 it would melt at  1084+327\2=705(???)C and would probably have the hardness of 2.25 (?) And about the historical axes and other bronze stuff,i knew that tin,arsene was used most often,with 1-2% lead added to sword bronze for easier hammering,sharpening.The casting will be surely captured;the bellows are in a phase that one bellow is a sheep skin without fur and the other one still has fur Made 2 ~250ml crucibles and a small ~50ml one,from clay with 1\3-1\4 sand in it,still have to be fired,on the left there's the blowing nozzle of the bellows system already fired and a lost wax small scythian style axe mould with 75% or more sand so it won't crack at shrinking on the wax positive inside it,and a dagger mould which might not survive as it's pure clay and thick...The bellows and wood pipes are the next thing to make.The progress is slow,but it's progressing a bit weekly.

Jlasud, how is the bronze ax to be hafted? 

I have never actually looked up the boiling point of lead, most reloading and bullet casting books say that lead starts to sublinate at about 10 degrees above its melting temp, so you really have to watch for lead fumes.  Most bullet alloys are lead, antimony and tin, the antimony for hardness and the tin for castability.  It makes the liquid fill out the small angles and then shrinks so the bullet releases cleanly from the metal mold.  Bill

Yes,Bill the axe is a shaft hole version,it has clay rod in the mold,which will be broken after casting.I melt lead at home,with the hood turned on,the heat rises any fumes directly into the hood ,and i don't stay around it until it melts,then i cast.

Hallo Bill!
If I've understood your question correctly, they didn't cast from the top, because carving such an item on a block of stone was hard work.
If you think to moulds that have survived, they are all thought for items that had the same thickness. Such an axe has a regular thickness, but the cylinder increases it.
So it's easier to make a wax model, than to carve the cylinder in the stone, even because the heat would probably break the "inside" of the cylinder 
I hope that I explained myself!
Greetings,
Mauro.