That's an interesting idea, especially if you could guarantee—through proper propellant selection—that a wadcutter made Zamak 3 would reliably produce a muzzle velocity of 1,000 fps.
According to this source, the density of Zamak 3 alloy is 6.6 grams/cm
3:
http://www.matweb.com/search/DataShe...0a2bc79&ckck=1
The density of Lyman's No. 2 hard-cast 5% antimonial alloy is 10.80 grams/cm
3:
http://www.matweb.com/search/DataShe...10b872dd61923e
This suggests that a 148-grain .38-caliber wadcutter, if cast from Zamak 3, sized at 0.3575'' would drop from the mould with a mass of 90.45 grains.
With a muzzle velocity of 1,000 fps, the predicted penetration of a 0.3575'' 90.45 grain wadcutter in soft tissue would be—
Q-model: 12.93 inches
mTHOR model: 14.61 inches
MacPherson WTI model: 15.32 inches
The compressive yield strength of 5% antimonial lead alloy is 24.5 MPa as opposed to 415 MPa for the Zamak 3 alloy which should make the Zamak wadcutter much less likely than its lead counterpart to deformation against hard tissues like bone. At 1,000 fps, a strike against bone would result in a pressure on the order of 100 MPa, so it is probable that the Zamak projectile would not deform upon striking bone.