Another note: a big-name High Power shooter once wrote that he was checking his shooting log when he realized that his basic zero for long-range shooting on his rifle was now two minutes higher than it had been the season before. While his rifle was still shooting “X” ring accuracy, it clearly had a worn throat. (How is this obvious? When the bullet moves forward, it slows at the impact with the rifling.
That increases pressure, and velocity. His bullets were traveling further forward, getting less of a spike, and thus shorted on velocity. Less velocity meant more clicks up to hit the target at distance.) There was no way of telling how much useful life was left in the barrel, when the barrel would quit and stop shooting accurately. Accurate record-keeping allowed him to change the barrel before accuracy went away.
Most problems can be solved by one of the four problem areas discussed later, and rarely will a rifle need more than attention to the “Big Four”:
Weak extractor spring
Lack of lubricant
Loose carrier key
The charging handle and carrier-bolt assembly can be installed in the upper before or after you connect the upper and lower receivers with the front take-down pin. If you install them before, insert the charging handle into the upper receiver.
Then press it upwards until it stops against the inside. Move it forward and back in the top track until the retention flanges on the charging handle drop into the access slot cut in the track. Then press the charging handle forward halfway. (If it drops, or tries to drop out, you missed the access slot. Try again.)
Take the carrier-bolt assembly. Make sure the bolt is fully forward by snapping your hand forward while holding tightly onto the carrier. The bolt, if not all the way forward, will slap forward to full extension. Insert the gas key into the charging handle recess and press the carrier forward.
Once it reaches the charging handle, the carrier will push the charging handle ahead of it. Press the carrier and charging handle fully forward, until the charging handle latch catches on the receiver. (There is a slot machined on the receiver for it to latch onto.)
Close the dust cover door. The charging handle latch, and the dust cover door, have enough retention to keep the carrier in the upper against gravity. However, if you have the rear of the upper receiver pointed down and something jars the upper, the catches may not hold. So while you have the upper off the lower, keep the muzzle level or pointed muzzle-down to keep the parts in.
Place the front takedown lug of the upper in between the flanges of the lower, and press the takedown pin from right to left to secure the upper. Then hinge the lower down until it is closed and press the rear pin across.
This article is an excerpt from Gunsmithing The AR-15
You’ll Love This If:
- You own an AR-15 and want to learn how to fix or upgrade it yourself
- You’re a professional gunsmith or are studying to become one
- You want to maintain your AR-15 for years of rugged, dependable use