Please show us in the Mil spec where every individual bolt and carrier is MPI'd. Typically in mass production the QC system will test or inspect a statistically significant proportion of a production run. It is very rare to use 100% inspection rate.
Every Colt, Colt Canada and FNMI M16 bolt must be HPT and MPI. The MILPSEC is clear: 100%. In order to qualify MILSPEC the testing must be performed with detailed records and within access of a government inspector.
Canada adheres to US MILSPEC except where Canadian Specs exceed US - for example accuracy acceptance testing: 2 MOA vs 4MOA MAX.
MIL-R-63997B (AR)
Military Specification Rifle, 5.56MM: M16A2
3.4.4
High pressure resistance.
Each barrel assembly and bolt shall withstand the firing of one Government standard M197 5.56 mm high pressure test cartridge conforming to MIL-C-46936. After proof firing, all parts shall be free of cracks, seams and other injurious defects as evidenced by visual and magnetic particle inspection. Testing shall be specified in 4.5.3.1, T III
Table III
High pressure resistance sample:
%100
4.7.4.2
Barrel inspection. The barrel assembly shall be magnetic particle inspected in accordance with MIL-STD-1949 utilizing a current of 400 to 500 amperes for circular continuous magnetization. The barrel assembly shall be examined for evidence of cracks, seams and other injurious defects.
4.7.4.3
Bolt inspection. The bolt shall be magnetic particle inspected in accordance with MIL-STD-1949 utilizing standard five turn magnetizing coil with a current of 200 to 300 amperes. Both circular and longitudinal continuous magnetizing with wet fluorescent solution shall be used. The bolts shall be examined for evidence of cracks, seams and other injurious defects.
4.7.4.4
Proof markings. Proof marks and magnetic particle inspection marks
shall be applied on barrel assemblies and bolts that have passed this test.
It's actually a pretty simple test to perform. I've been present and observed it in person in several production facilities. Granted, it is expensive to perform this test and record it and audit it for EVERY single bolt. There is a reason why the testing was insisted on and continues to be for all military small arms. Considering that the stoner system is designed to contain over 100,000 PSI in the chamber, extension and bolt, I would feel much better putting my head beside one that was made properly, heat treated properly and 100% verified.
The MILSPEC also goes on to note that ALL components will be made with the materials and processes specified in the TDP with no exceptions. The materials and heat treating are verified by government inspectors and the records audited by ISO and NATO AQAP as well.