Is an M4 barrel really actually truly 14.5" long?

[TED]

I believe the ATF measures from the closed bolt face.

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Yes, that's right the ATF measures from the closed breech face.

So then, from the closed breech face what is the length of an M4 barrel without a muzzle device?

This could be an important detail for people when doing a pin and weld muzzle device.

TED

[Iraqgunz]

The ATF procedure for measuring barrel length is to measure from the closed bolt (or breech-face) to the furthermost end of the barrel or permanently attached muzzle device. Permanent methods of attachment include full-fusion gas or electric steel-seam welding, high-temperature (1100°F) silver soldering, or blind pinning with the pin head welded over. Barrels are measured by inserting a dowel rod
into the barrel until the rod stops against the bolt or breech-face. The rod is then marked at the furthermost end of the barrel or permanently attached muzzle device, withdrawn from the barrel, and measured.

[Clint]

Here is an example calculation for our 14.5" MPC barrel.

The conservative approach is to target the total length just over 16" and keep the extra length gained by the ATF method in the bank.

Pro Tip: Most advertised "16 inch" AR barrels are actually 16.125" from breech to muzzle.