Player not taking damage with hit collidor

I'm very new to unity, and currently i'm trying to get my player to take damage from shots fired (Raycasts) from an enemy NPC. What currently works is that the player can damage the enemy NPC's when fired, but it doesn't work the opposite way, and i can't seem to figure out why.

Gun Class:

 using UnityEngine;
 using System.Collections;
 
 [RequireComponent (typeof (AudioSource))]
 public class Gun : MonoBehaviour {
 
     public enum GunType {Semi,Burst,Auto};
     public GunType gunType;
     public float rpm;
     public LayerMask collisionMask;
     public float damage = 1;
 
     // Components
     public Transform spawn;
     //public Transform shellEjectionPoint;
     //public Rigidbody shell;
     private LineRenderer tracer;
 
     // System:
     private float secondsBetweenShots;
     private float nextPossibleShootTime;
 
     void Start() {
         secondsBetweenShots = 60/rpm;
         if (GetComponent<LineRenderer>()) {
             tracer = GetComponent<LineRenderer>();
         }
     }
 
     public void Shoot() {
 
         if (CanShoot()) {
             Ray ray = new Ray(spawn.position,spawn.forward);
             RaycastHit hit;
 
             float shotDistance = 20;
 
             if (Physics.Raycast(ray,out hit, shotDistance)) {
                 shotDistance = hit.distance;
 
                 // just testing here, dont mind this!
                 if(hit.transform.tag == "Player") {
                     Debug.Log ("Player Hit");
                 }
 
                 if(hit.collider.GetComponent<Entity>()) {
                     Debug.Log("Taking Damage");
                     hit.collider.GetComponent<Entity>().takeDamage(damage);
                 }
 
 
             }
 
             nextPossibleShootTime = Time.time + secondsBetweenShots;
 
             audio.Play();
 
             if (tracer) {
                 StartCoroutine("RenderTracer", ray.direction * shotDistance);
             }
 
             //Rigidbody newShell = Instantiate(shell,shellEjectionPoint.position,Quaternion.identity) as Rigidbody;
             //newShell.AddForce(shellEjectionPoint.forward * Random.Range(150f,200f) + spawn.forward * Random.Range(-10f,10f));
         }
 
     }
 
     public void ShootContinuous() {
         if (gunType == GunType.Auto) {
             Shoot ();
         }
     }
 
     private bool CanShoot() {
         bool canShoot = true;
 
         if (Time.time < nextPossibleShootTime) {
             canShoot = false;
         }
 
         return canShoot;
     }
 
     IEnumerator RenderTracer(Vector3 hitPoint) {
         tracer.enabled = true;
         tracer.SetPosition(0,spawn.position);
         tracer.SetPosition(1,spawn.position + hitPoint);
 
         yield return null;
         tracer.enabled = false;
     }
 }

Entity class, which Player.cs and Enemy.cs extend:

 using UnityEngine;
 using System.Collections;
 
 public class Entity : MonoBehaviour {
     // this class will model our enemies
     // enemy health
     public float health;
 
     public virtual void takeDamage(float dmg) {
         // subtract dmg points from health
         health -= dmg;
         // log it
         Debug.Log (health);
 
         if(health <= 0) {
             // kill enemy
             die();
         }
     }
 
     public virtual void die() {
         // log that enenmy is dead
         //Debug.Log ("Dead");
         // destry the game object
         Destroy (gameObject);
     }
 }

And the Enemy.cs class;

 using UnityEngine;
 using System.Collections;
 
 public class Enemy : Entity {
     // add player expereicne points
     public float expOnDeath;
     // get reference to player
     private Player player;
 
     void Start() {
         // find the game object with player tag
         player = GameObject.FindGameObjectWithTag ("Player").GetComponent<Player>();
     }
 
     // override base die method, but with added functionality
     public override void die() {
         // add exp points
         player.AddExpereince (expOnDeath);
         base.die ();
     }
 }

And the player.cs class

 using UnityEngine;
 using System.Collections;
 
 public class Player : Entity {
 
     private int level;
     // current exp level
     private float currentExpLevel;
     // exp required to level up next
     private float expToLevel;
     public GameGUI gui;
 
     void Start() {
         gui = GameObject.FindGameObjectWithTag ("GUI").GetComponent<GameGUI> ();
         // by default the players level will be set to 1
         LevelUp ();
     }
 
     public override void die() {
         base.die ();
     }
 
     public void AddExpereince(float exp) {
         currentExpLevel += exp;
         if(currentExpLevel >= expToLevel) {
             currentExpLevel -= expToLevel;
             LevelUp();
         }
         gui.setPlayerExp (level);
         //Debug.Log ("EXP: "+currentExpLevel+" Level: "+level);
     }
 
 
     private void LevelUp() {
         // increase exp level
         level++;
         expToLevel = level * 50 + Mathf.Pow (level * 2,2);
 
         AddExpereince (0);
     }
 }