Most fullsize offroad bikes use 520 chains. You can use a non-oring chain but it will wear out much, much faster. I always use some sort of o-ring, x-ring, etc chain. Have used Regina chains for years.
I have run RK X ring chains for a while and they rock ! I've trashed them thru mud, sand, rocks and combinations of all three never had a failure. They cost a bit more than an oring but totally worth it.
if you are on a budget you can use some sort of Steel sprocket (around $15-$20) and china made 520 o-ring chains if you manage to find any (around $30) but both sprocket and chain last.