How to Troubleshoot an AR15

Place the rifle on a clean, flat working surface to examine it. Remove all live ammunition from the area. Wear safety goggles to protect against spring-loaded parts, which might eject or fly out from the weapon.

Clear the chamber of the rifle and remove the magazine before inspecting the weapon. Put the safety switch in the "On" position, then push the magazine catch button. Drop the magazine. Pull the charging handle rearward, then press the bottom of the bolt catch. Return the charging handle to forward and check the chamber. Remove any live cartridge.

Push the receiver pivot pin inward. Check your service manual for its location. Pull back on the charging handle to remove the bolt carrier and bolt. Take out the firing pin retaining pin by pulling it out and downward. Let the firing pin drop from the bolt carrier onto one hand and inspect it for cracks and deformities. The firing pin is a likely miss-fire component.

Take out the extractor and spring, according to directions, but leave the spring attached to the extractor. Look for carbon buildup and wear on the extractor surface near the end lip. The lip should have no cracks or worn edges. A worn or chipped extractor and weak spring will cause an ejection-extraction failure. Both pieces must be clean and lubricated. Check the extractor claw for burred edges, and evidence of any brass shavings blocking the ejector pocket.

Check the magazine latch, if the magazine fails to lock into the rifle. The magazine catch should have no excess wear, rust or debris on it. Check for a broken magazine catch spring. Also determine if too many rounds have been loaded into the magazine at one time, forcing too much pressure on the catch mechanism.

Check the magazine buffer spring operation and its freedom of movement, if the rifle auto-feed fails to load subsequent rounds. If the buffer spring is an aftermarket version, it might be too short to supply enough feed pressure. Check your parts service manual for the correct size and length of the spring. Look for any dirt or obstruction inside the magazine housing, which could cause the cartridges to hang up and stick.

Look for a bent or damaged gas tube if the rifle fails to automatically chamber a round. Make certain the ammunition is standard, and recommended for the rifle. Customized loads can sometimes refuse to load, or cause excessive or inappropriate breech pressure.

Check for the presence of the bolt cam pin, if the action fails to lock. Check your service manual for its location. The bolt cam must be present. Examine the barrel locking lugs for heavy carbon buildup, dirty grease or rust and corrosion. The lugs must be free of all debris and remain clean and lubricated. Check for a loose magazine, even if the catch engages properly. The catch mechanism can be worn, causing excessive play and misalignment.

Examine the firing pin hole or the pin recess on the rifle bolt for carbon blockage, if the rifle fails to fire. The firing pin should have a uniform blunted head, with no evidence of mashed metal on any side, chips, or a flattened or mushroom head. Look for a missing or broken firing pin retaining pin. Work the selector lever back and forth, to ensure that it has not frozen in the "Safe" position.

Check for proper lubrication of the bolt and receiver mechanism, if the rifle experiences short recoil or short stroking. Short stroking in the bolt carrier can be caused by a loose bolt carrier key, misalignment of the gas tube at the base of the front sight, broken bolt rings or a dirty receiver extension or action spring.

Check the rifle barrel for a loose barrel nut, if the rifle fails to zero in properly on a target. Examine the front and rear sight assembly mechanisms for cracks and any bent appearance on the shrouds or bead sights.