AO Precision C158 SP/HPT/MPI 5.56 Bolt Carrier Group – Black Nitride




AO Precision has provided BCGs to large military contractors such as FN America and large commercial retailers who re-brand and sell these at a considerable mark-up.


Machined from Carpenter Technology No. 158 alloy.
Heat treated
Shot peened per ASTM B851/SAE AMS2430S
Individually High Pressure Tested (test fired)
HP proof testing, 100% using a high pressure M197 or SAAMI commercial equivalent, without evidence of failure
Individually Magnetic Particle Inspected after Initial Test Fire
Manganese Phosphate Finish

4140 Steel per ASTM A108, cold drawn and stress relieved BHN 187-22
Phosphate Finish
Extractor Spring
Black Extractor Insert
Viton O-Ring

Machined from AISI 8620 aircraft quality alloy per ASTM A108/A322-13
Full Mass M16 Profile
Stress Relieved
Black Nitride Finish
Gas Key

Machined from 4130 chromoly steel alloy per ASTM A108/A322-13
Grade 8 Hardware
Properly Staked
Hard Chrome Internal
Permatex sealed


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