Added all four gun types and firing bullets stable (although there is some slight 'recoil' for some variations)

Assets/Prefabs/Bullet.prefab

@@ -92,7 +92,7 @@ Rigidbody2D:
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   m_PrefabAsset: {fileID: 0}
   m_GameObject: {fileID: 6732034634797273297}
-  m_BodyType: 0
+  m_BodyType: 1
   m_Simulated: 1
   m_UseFullKinematicContacts: 0
   m_UseAutoMass: 0
@@ -143,4 +143,3 @@ MonoBehaviour:
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   m_Name: 
   m_EditorClassIdentifier: 
-  speed: 5

Assets/Prefabs/Obstacle.prefab

@@ -15,7 +15,7 @@ GameObject:
   - component: {fileID: 7683230909844016913}
   m_Layer: 0
   m_Name: Obstacle
-  m_TagString: Untagged
+  m_TagString: Obstacle
   m_Icon: {fileID: 0}
   m_NavMeshLayer: 0
   m_StaticEditorFlags: 0
@@ -130,7 +130,7 @@ Rigidbody2D:
   m_PrefabInstance: {fileID: 0}
   m_PrefabAsset: {fileID: 0}
   m_GameObject: {fileID: 6511841225854600656}
-  m_BodyType: 2
+  m_BodyType: 0
   m_Simulated: 1
   m_UseFullKinematicContacts: 0
   m_UseAutoMass: 0