The 38 may be a softer alloy, then a mag 357 lead bullet.
Bullet alloy may be matched to a box of ammo. If the ammo is still in possession of the bad guy.
FBI https://archives.fbi.gov/archives/a...cience-communications/fsc/july2002/peters.htm
Example
metal wt. %
______________________________________
Copper 0.038
Arsenic 0.16
Antimony3.0
Tin 0.25
Zinc 0.0001
Cadmium 0.0001
Nickel <.0001
Bismuth 0.018
Silver 0.0038
Tellurium 0.0015
Sulfur 0.0005
Iron <.0001
Lead Balance
This "theory" has been discredited.