The LA-SF15 upper receiver comes with a Picatinny rail system which gives you the flexibility to mount any optics or accessories to enhance your shooting experience. It's precision machined to ensure perfect alignment and a snug fit with the lower receiver resulting in superior accuracy and consistency. This upper receiver also includes a forward assist and dust cover providing reliable function in harsh conditions.The LA-SF15 lower receiver on the other hand includes features that enhance ergonomics and ease of use. It comes with a flared magwell for faster and easier magazine changes and a tension screw for a snug fit with the upper receiver. The lower receiver is also fully compatible with standard AR-15 parts and accessories offering unlimited customization possibilities. This set gives you a high-quality starting point to build the AR-15 of your dreams.