HELP> What is this sphere made of and what was it for?

My son in law found this item on Charmouth beach in Dorset, which is on the south coast of England last weekend during a fossil hunting day out with four like minded friends. It was found on a pebble beach near to the waters edge, which is the English Channel.

It measures 1-1/8" (28.6mm) in diameter and weighs 34.15grms. It cannot be steel as a ball bearing of the same diameter weighs 95.68grms.

Therefore we are trying to ascertain the material and possible use. (i.e. Was it from any sort of gun). Unlikely as it does not appear to be metal

Whilst taking the above photographs this morning, it did roll across my table, and it sounded like a piece of stone, but that is my best guess.

We now pin our hopes on the experts of the world

You are probably right - round shots packed in to cannonballs 

Your data suggests this material has about ⅓ the density of iron. In fact,  the density of granite falls in that range.

Pebbles tumbled in river runoff of rough surf for many years, can become very round.

I think it is a natural phenomenon.

So,

They might pack a cannon with these items and just fire it! What sort of damage would it do to the ship and would they kill sailors?

It is getting very interesting.

Based on my knowledge from movies - the stuffing of nails in crude bombs was intended to inflict damage & pain.

I think stones if used as shot would be smashed to powder in the process, and not travel far.

So, the enigma continues. I have done a few searches, but nothing of interest found