proper fire hardened clay is actually really tough.
Christian and uwe have been using them at the international for a few years.
Uwe throws harder than christian, but even so unless you hit the metal centre they usually survive just hitting the wood.
weight wise - what are you guys throwing ?
A 40mm ball of modelling clay weighs in at around 60-70gms - the perfect ammo both for diatance and target.
40mm is a great size (little smaller than a golf ball) great density and a 15kg bag of air dry modelling clay - which is stiffer and denser than potters clay - will yield up about 215.
And very fast to roll by hand.
That's what i threw at hodd hill - approx 2000plus throws in 2 days, plenty of headshots and body shots at 50 metres. And of the 150 or so balls peter made I brought about 3/4 of them home.
The rest are forever a part of the hillforts banks.
But unless you hit a very hard target - they are extremely durable and can be re-used many timnes.
Particularly if you use bright orange outdoor paint
So just make a soft target.
Jaegoor is partially right. Cement is hard to work with - the key is getting the consistency right. Very fine sand with pva glue and shredded newspaper, is your friends there.
But it is much cheaper than modelling clay and doesn't shrink quite as much on setting.
While Not being lawnmower friendly they are heavier and tougher than clay. And not toxic to the environment.
Stones are - for my mind - too hard to get, too prone to breaking and definitely NOT friendly to either lawnmowers or dogs. They break into slivers of razor sharp shards.
There is probably nowhere in the uk you could use stones on a metal target without risking cutting a dogs or wild animals paws.
Obviously they don't care about any of this in the balearic islands and competitions are frequently held on land the public and their dogs have access to.
The whole macho thing is the real sticking point.
Historically - if you did not live on the coast - clay would have most likely been your ammo of choice.
But morphy try the 'modelling' cement.
You'll have to wing the pva and shredded newspaper content to sand and cement. But I can;t see any issues you should be able to get a really nice firm but malleable consistency. That would actually suit my moulds better than the clay i use - squashign that stuff into shape is a real workout.
The main reason the moulds are so massively over-built