Hey, I am making a mod and I want to add a Gun that will cause damage to entities or other players. However I cannot find how I can get the entity the player is looking at. I tried

public ActionResult<ItemStack> onItemRightClick(ItemStack itemStackIn, World worldIn, EntityPlayer playerIn, EnumHand hand)
{

	RayTraceResult mop = Minecraft.getMinecraft().objectMouseOver;
                if(mop != null){
                   System.out.println(mop.entityHit);
                       }
}

but it doesn't work if the player is away from the entity (It displayes the entity when the player has the "Village-Player trade" distance). Does anyone know how I can make it?

You will have to make your own instance of MovingObjectPosition using Vectors.

or use World#rayTraceDo(...) or whatever its named.

it doesn't work if the player is away from the entity (It displayes the entity when the player has the "Village-Player trade" distance). Does anyone know how I can make it?

 

The raytrace done every tick ignores entities that are not within 3 blocks of the player, as you suggested. Like Draco says, you're going to have to do a manual ray trace. However, entities provide a function for ray traces that takes into account rotation and eye height, so you don't have to do it manually. You can see how vanilla sets mc.objectMouseOver in EntityRenderer#getMouseOver, which uses the said ray trace method. If you just want to extend the range, I believe you only have to change 1 number

Thanks everyone for their help. I just copied the method from the EntityRenderer and changed some variables! Now It works perfectly!  ;D