Metal Detecting

I've been hitting the beaches lately and found about 5 or 6 fist-sized lumps of concretion on the low tide. I've been wondering how to get them open to see what's inside. I don't want to smack them with a hammer just in case there's something nasty inside that might explode on me! I found some shrapnel not a million miles away so I'm a bit wary.

What do other detectorists do with these cruddy old lumps?

I use a vice for full control, with angled jaw attachment. Ball Pein otherwise!

Always done on the beach to avoid my flying limbs damaging the shed at home.

I have a very close friend who cracked open such a lump only to reveal what was once a live hand grenade, in pieces + original contents; really lucky to be alive!

I think I'll leave them well alone from now on then!!!

I have a pic of said item somewhere and will post once I have dug it out from my files. (sorry about the pun!)