What Is An Upper Receiver?
Upper receivers are the top half that marry the lower half of an AR style rifle, also known as the “lower receiver”. Within the upper receiver are various parts for your AR-9, AR-10 or AR-15 being housed including the bolt carrier group, charging handle, dust cover and forward assist button. The rear of the upper receiver connects to the buffer tube and the front of the upper receiver connects the barrel, gas tube and handguard.
The upper receiver, commonly referred to as just the "upper", is the heart of your rifle. It's where all the most performance critical components of your rifle lay. Your barrel choice will affect everything from accuracy to reliability to recoil impulse (depending on it's gassing). Your gas system, and bolt carrier group (or BCG, for short), will also play a crucial role in your reliability and felt recoil from the gassing of your rifle.
An upper receiver is no place to cheap out on parts, and that's why we only carry quality parts at Modulus Arms. Every part you see for sale is something that we know to work well, from our own experience as shooters, and we're happy to answer questions about any of them!