Before you inspect
Clear the rifle, remove the magazine, lock the bolt to the rear, and physically check the chamber. Inspections are performed on an empty rifle in a safe environment with good lighting.
Bolt Inspection
The bolt is the highest wear safety critical part in the rifle. Inspect it at every cleaning and replace on schedule, even if it looks fine.
Crack locations
What to look for
Look at the cam pin hole, the radius behind the lugs, and the lug roots. Use a magnifying glass or loupe. Clean the bolt first so cracks are visible.
When to stop shooting
Any visible crack means retire the bolt immediately. Do not fire the rifle.
Lug wear patterns
What to look for
Locking lugs should show even contact across all seven lugs. Uneven wear or galling on one or two lugs indicates uneven headspace or excess pressure.
When to stop shooting
Chipped or sheared lugs require immediate replacement. Any lug missing material is unsafe.
Gas ring test
What to look for
Stack the three gas rings with their gaps aligned. Assemble the bolt into the carrier, extend the bolt, and stand the BCG on its head (bolt down). If the bolt falls under its own weight, the rings are worn.
When to stop shooting
Failed gas ring test causes short stroking and failures to cycle. Replace rings before next range session.
Extractor and spring
What to look for
Extractor should snap back crisply. Spring should show no collapse. The o-ring (if equipped) should be intact and not flattened.
When to stop shooting
Weak extraction causes double feeds and failures to eject. Replace on schedule.
Barrel Inspection
Barrels are consumable. Accuracy degrades long before the barrel is unsafe, but catastrophic failures are rare and usually telegraphed.
Throat erosion
What to look for
Use a throat erosion gauge or borescope. Heavy pitting or alligator skin texture at the throat indicates heat damage. Precision shooters track this with MOA degradation.
When to stop shooting
Severe erosion does not typically make the barrel unsafe, but accuracy drops sharply. Replace for precision use.
Crown damage
What to look for
Inspect the muzzle end of the rifling. The crown should be uniform, with no dings, burrs, or asymmetric wear. Damaged crowns open groups dramatically.
When to stop shooting
A dinged crown is an accuracy problem, not a safety problem, unless part of the muzzle is cracked.
Bore condition
What to look for
After cleaning, inspect the bore with a borescope or flashlight. Copper streaks, pitting, or ringed bulges are serious. Ringed bulges indicate a squib was fired through.
When to stop shooting
A bulged barrel is unsafe. Do not fire. Replace the barrel.
Receiver Inspection
Aluminum receivers wear slowly. The main wear points are the takedown and pivot pin holes, the buffer tube threads, and the rail mounting surface.
Pivot and takedown pin holes
What to look for
Holes should be round with minimal elongation. Excessive wallow causes the upper to wobble on the lower.
When to stop shooting
Not typically unsafe, but severe wear degrades accuracy and reliability. Consider receiver replacement.
Buffer tube threads
What to look for
Threads should be clean and sharp. Cross threaded or stripped threads cause the castle nut to back off and the buffer tube to shift.
When to stop shooting
Stripped threads are a safety issue. The buffer tube can separate from the receiver during firing.
Rail mounting surface
What to look for
The Picatinny rail on the upper should be flat and undamaged. Dents, burrs, or bent slots cause optic mounting issues and loss of zero.
When to stop shooting
Usually an accuracy problem. Check that mounted optics are torqued properly.
Gas System
The gas system rarely fails, but when it does the rifle stops cycling. Inspect every few cleaning cycles.
Gas block alignment
What to look for
With the handguard off, verify the gas port on the barrel lines up with the gas port in the gas block. Misalignment causes short stroking. Check that set screws or cross pins are tight.
When to stop shooting
Loose or misaligned gas block causes reliability issues. Not typically a catastrophic safety problem.
Gas tube condition
What to look for
Gas tube should be straight with no visible kinks or crushed sections. The tube should sit flush in the upper receiver when the BCG is installed.
When to stop shooting
A bent or crushed gas tube must be replaced. A gas tube that binds on the BCG causes carrier tilt and carrier damage.
Trigger Group
Fire control groups are simple, but a worn or damaged trigger group is a direct safety issue. Function check after every cleaning.
Sear engagement
What to look for
Cock the hammer, apply light pressure to the trigger without pulling. The hammer should not drop. Sear surfaces should be sharp and unworn.
When to stop shooting
A trigger that drops the hammer on safety release or bump is unsafe. Replace the fire control group immediately.
Disconnector function
What to look for
Hold the trigger to the rear after firing (dry fire). The disconnector should catch the hammer. Release the trigger: the disconnector should hand the hammer off to the trigger sear with a crisp reset.
When to stop shooting
A failed disconnector can cause doubles or runaway fire, which is unsafe and illegal in most semi auto configurations.
Hammer spring
What to look for
Hammer should fall with authority. A weak hammer spring causes light primer strikes. Coils should be intact with no visible kinks.
When to stop shooting
Light strikes are a reliability problem, not typically unsafe. Replace the spring.
Need replacement parts?
If your inspection flagged any items, shop replacements through the builder or check your round count against the service schedule.
These are recommended intervals based on published military maintenance schedules and manufacturer guidelines. Your specific maintenance needs may vary based on ammunition, environment, and use conditions. When in doubt, consult a qualified armorer or gunsmith.