52-54d.
Pay close attention to the date codes. Some "new" ones may not be as new as you think (depending on your supplier.)
If you need them harder, open them up (sand or cut) and let them sit and cure (longer the better.) You can also manipulate the heat cycles by putting them in a hot box and cycling the heat (up and down) several times over. That and wiping them with methanol, simple green, etc, will help speed up the process, but nothing beats good old time for hardening.