(Continued from Part 1. This concludes the article.)
The mid-length and rifle length gas systems are known for operating the action more smoothly when compared to the carbine length system. The mid length gas system increases for the carbine length barrel. The longer gas tube gives a longer bolt carrier dwell time in the rifle, which lets all the moving pieces work a little more slowly and less violently but still quickly and energetically enough to let the bolt carrier move back fully and allow the bolt to strip the next round off of the magazine reliably. The entire recoil system is stressed less, reducing wear and tear and malfunctions during normal conditions.
The bolt carrier group contains the bolt, bolt cam, gas key, and the firing pin. For this vital part I try to keep it simple. A steel, mil-spec bolt carrier group from a quality manufacture is often the best answer and is a proven performer. Good ones are often tested using Magnetic Particle Inspection during manufacture to look for defects. The bolt can be purchased separately from the bolt carrier but is normally purchased as part of a high quality bolt carrier group.
The upper receiver is the M4 version which has a factory M4 Picatinny top rail to support the rear sight and the scope base. It should also have enhanced M4 cuts for the feed ramps, which are machined at a shallower angle. This newer feed ramp angle is much more forgiving during the feed cycle and easier on the nose of the bullet. Almost any upper from a reputable dealer will work well.
The lower receiver has the serial number, contains the trigger group, supports the buttstock, and houses the magazine. The trigger mechanism has a disconnector that keeps the rifle from firing more than one shot per pull of the trigger. The proper operation of the disconnector function is critical to safety and should be verified before the rifle is fired.
There are three common types of buttstocks, the telescoping or collapsible, the fixed A1 length, and the fixed A2 length, with the A2 length being the longest. I like the A1 length with a trapdoor that lets you store a few things in it, thereby keeping those things with the rifle at all times. One such item should be whatever needed to remove and replace the scope base from the upper receiver. Another should enable you to install the rear backup iron sight if it has been stored in the buttstock compartment.Continue reading“Thoughts on a General Purpose AR-15 Rifle – Part 2, by Steve A.”