Freeze Plug blowing out

Just redid The #match 340 in my dads 72 Duster
1st run after ring break in and look over blew the right side front freeze plug right out of the block with a heavier acceration.
Got it home and installed another brand new one
took it out got on it and blew it again
Can anyone help us out?
They fit super good
1st rebuild he is the original owner
Thanks in advance
Mike Z.