So what does Mil-Spec mean???

[jmart]

Here is the short list:

Barrel Steel: 4150ORD, 4150SUL or CMV
Bolt Steel: 154 Carpenter
High pressure testing: Both bolt and barrel
Magnetic Particle Inspection: Both bolt and barrel
Barrel Extension: M4
Upper Receiver: M4
Gas key: Properly Staked
Castle Nut: Properly Staked
Receiver Extension: Mil-Spec 7071 impact extrusion
Buffer: H, H2 or H3 (depending on barrel length and type of gas system)
Gas port size for a Carbine: .063
FSB: Rated for flat top (F stamped)
Chrome Lining: Yes
Twist rate: 1/7 (handles everything from 55gr to 80gr well)
Chamber: 556 NATO

C4

There's a whole history of where BM, RRA, etc. fall short on several items on this list, but where do they fall WRT gas port diameters? Are they spec? If not, how much over or under?