KNU_SpaceShooter/Assets/02_Scripts/Barrel.cs

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

public class Barrel : MonoBehaviour
{
    private GameObject expEffect;
    private int hitCount = 0;

    void Start()
    {
        expEffect = Resources.Load<GameObject>("BigExplosion");
    }

    void OnCollisionEnter(Collision coll)
    {
        if (coll.collider.CompareTag("BULLET"))
        {
            if (++hitCount == 3)
            {
                Instantiate(expEffect, transform.position, Quaternion.identity);
                var rb = this.gameObject.AddComponent<Rigidbody>();
                rb.AddExplosionForce(1500.0f, transform.position, 10.0f, 1800.0f);
            }
        }
    }
}