hibernate OneToMany composite key

I'm fairly new to hibernate and I am trying to create a Hibernate OneToMany mapping

It's using a composite key (int, int, int) on both parent and child tables.

I have tableA with column (x, y, z, name etc)
Table A contains
1, 2, 3, "tom"

I have tableB with columns (x, y, z, other etc)
Table B contains
1, 2, 3, timestamp, amount
1, 2, 3, timestamp2, amount2
1, 2, 3, timestamp3, amount3

Instead of returning one record from table A (with a set of 3 B records) when I restrict on Restrict.idEq(key)

it is returning the number of records in my "B" table ie
1,2,3,"tom",1, 2, 3, timestamp3, amount3
1,2,3,"tom",1, 2, 3, timestamp3, amount3
1,2,3,"tom",1, 2, 3, timestamp3, amount3
(It seems to only return the most recently added record in B ie timestamp3, amount3)

This is my set up

My embedded class is as follows
@Embeddable
public class MyKey implements Serializable {
    private int x;
    private int y;
    private int z;

The A class is
@Entity
@Table(name="tableA")
public class A implements Serializable {
    @Id
    private MyKey key;
    private String name;

    @OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER)
        @JoinColumns ({
        @JoinColumn(name="x", referencedColumnName = "x", insertable=false, updatable=false),
        @JoinColumn(name="y", referencedColumnName = "y", insertable=false, updatable=false),
        @JoinColumn(name="z", referencedColumnName = "z", insertable=false, updatable=false)
    })
    public Set<B> set;

The B class is
@Entity
@Table(name="tableB")
public class B implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    private MyKey key;
    @ManyToOne
    @JoinColumns ({
            @JoinColumn(name="x", referencedColumnName = "x", insertable=false, updatable=false),
            @JoinColumn(name="y", referencedColumnName = "y", insertable=false, updatable=false),
            @JoinColumn(name="z", referencedColumnName = "z", insertable=false, updatable=false)
        })
    public A a; //unidirectional

So long as there is there is just one record in B for every record in A it seems to work.

But when I duplicate (many) records in B (in this case 3 records) and I try to retrieve
I get multiple A records! Each A record has a "set" of B records with just one B record!

Aside:
I started thinking the secondary table B should have a unique primary key by adding in timestamp
But when I did that I got the error: timestamp must be insertable: false, updateable: false
When I added timetamp to the JoinColumns I got the inevitable error: Unable to find logical column: timestamp in table A

So in summary it seems that my set-up is limiting me to one-to-one mapping

Similarly when I attempt to retrieve on B I get the error:
org.hibernate.HibernateException: More than one row with the given identifier was found: MyKey@a5843003, for class: B