Hey there, I'm new to ar15 rifles and need some help with my dpms ap4 carbine, I already have a magpul stock, forend, grip, rear flip up sight, and front forend sight. I want to next get rid of the stock gas block and put on a flat style for the magpul front sight, then a 45 degree mount for a holographic sight. So here are my questions 1. What gas block is best for this gun and the front flip up sight 2. What's the best holographic sight for 100$ 3. When I remove the stock gas block is the front ring that holds the forend going to stay there? Is it pressed on?