StickingBullet.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class StickingBullet : MonoBehaviour {

    //Add this to bullet
    //Creates a joint between bullet and the target it hits
    //Makes the bullet stick to its target.
    //Both need to have rigidbody

    bool hasJoint = false;

    void OnCollisionEnter (Collision collision) {

        if (!hasJoint) {
            gameObject.AddComponent<FixedJoint> ();
            gameObject.GetComponent<FixedJoint> ().connectedBody = collision.rigidbody;
            hasJoint = true;
        }
    }

}