06/03/2026
So its been some time since I posted much but between college full time, work full time and shooting full time; I have let my "Tales from the Gunsmith Workbench" fall short. However this project I could not resist posting.
So here is the basic:
Customer Complaint
AR-15 locked up during firing and could not be opened.
Findings:
Recovered fired .300 AAC Blackout case from a 5.56 NATO rifle.
Severe case deformation and brass flow.
Extractor ripped through case rim.
Extractor pin displaced and became lodged in the locking system.
Bolt required forced disassembly.
Case required removal with a rod after bolt separation.
Bold catch broke in half.
Inspection:
Barrel removed and inspected - Bullet exited the barrel!!!
Chamber inspected and cleaned.
Barrel extension inspected.
Headspace verified.
Damaged components replaced.
Outcome:
Rifle returned to service after inspection, replacement of damaged parts, and successful function testing.
After talking to the customer and explaining what happened he still was convinced the rounds were interchangeable and would not agree with my findings and said he must just have a bad barrel - YES THIS IS WHAT HE SAID AS HE PAID HIS BILL AND LEFT MY SHOP- He is lucky he did not get the BCG lodged in his forehead.
Lessons Learned300 AAC Blackout and 5.56 NATO are not interchangeable.
Ammunition should be positively identified before loading.
Surviving an ammunition mismatch does not mean it was safe.
