Precision/Varmint Rifle Build Part 2: Upper receiver selection
To understand what makes the AR-15 an accurate rifle, we must understand the design. One of the main contributing design elements that make this rifle platform so inherently accurate is the fact that the bolt locks up in a barrel extension, and not in the receiver like many bolt action rifles. In many rifle designs, the bolt locking lugs key into position within the receiver, and the barrel is threaded into, or clamped into the receiver using a nut. For a consistent and precise bolt lockup, a series of parts including the receiver, barrel, and bolt must be in perfect harmony. It can take quite a bit of work to make sure the bolt interface with the cartridge and receiver, the cartridge interface with the barrel and bolt, and the barrel interface with the receiver are all correct and true. That is where the AR-15 design shines. Since the bolt locks into the barrel extension, theoretically the receiver can be made out of anything, and as long as there is a solid bolt lockup, the barrel will shoot the same. Now that doesn’t mean the rifle will be accurate, it just means that the interface between the bolt, cartridge and barrel will not be affected.
For general purpose use, or even use with a non magnified optic, the standard mil spec forged upper will suffice, and give an adequate level of rigidity for practical accuracy. With that said, I am building a precision rifle that will be used to shoot varmints at distance, so practical accuracy will not do. When it comes to rifle accuracy, an often overlooked component is the upper receiver. While it is true that since the bolt locks up into the barrel, a quality barrel, and quality bolt should give exceptional accuracy, however, the scope is not mounted to the barrel, it is mounted to the receiver. Any amount of shift, vibration or flex between the barrel and upper receiver can affect consistent performance between the barrel and scope through the upper receiver. The more rigid and true the barrel, upper receiver, mount and scope are, the more consistent the rifle will perform.
I will be using a Northtech Defense billet stripped upper receiver for this build. The receiver is precision CNC machined from 7075 T6 billet aluminum to exacting tolerances, and features a mil spec hardcoat anodized finish. This receiver features heavier walls than a standard forged upper, and should offer a very rigid and precise platform to build on. The upper receiver will also be fitted with one of their excellent titanium forward assists.
As far as my choice for a charging handle, a standard mil spec handle and latch will work fine for this application. There are many enhanced charging handles on the market, and if i were building a 3 gun or defensive rifle, I would consider using such a handle (I prefer the Mega Arms Slide Lock), but since this rifle will be fired mostly from the prone position on a bi pod, The extra money could be used in other areas of the gun to a greater effect.
Read part 1 Here.