I'm looking to make my "M4" as light, durable, and reliable as possible. What do you guys recommend? It's a Bushmaster XM-15 E2S. I was thinking about a short rail on the factory handguards cause the most I'll ever put on it is a light, maybe doing a flip up rear sight instead of the carry handle, to save a bit of weight, and adding Night Sights, possibly a different grip and stock, but it had a Houge already and I don't see a need for a different stock. Is there anything internal I'm missing? 4 or 5" 100yd groups are fine with me in all honesty, I'm not in competition. Also, how are the Magpul BUIS rear sights, kinda like the price...