HM Defense Complete Threaded AR-15 Upper Monobloc 5.56

Questions & Answers

• Q: What is “ Head Spaced with GO and NO-GO Gauge Ready to Install on Your Lower”? I have a Franklin Armory BSFIII Equipped M4 223 Remington/5.56 NATO Lower Receiver……

  • Answered
  • Asked 04/26/2024 01:28 by Steve S

  A:

  It is a test of correct chamber dimensions (namely headspace) and fit of the bolt and barrel extension which is generally a standard practice by manufacturers. The gauges are meant to check whether the chamber is the correct depth to fit a cartridge of the SAMI specification size. If a go gauge does not fit in the chamber it has been reamed out too short and will not chamber and fire ammunition reliably if at all. If a go gauge fits in the chamber but a no-go (longer) gauge does not then dimensions are correct. If a no-go gauge does fit, the chamber is too deep which can cause split or ruptured cases, excessive parts wear, and a potential safety hazard. In this case they are saying headspace has been verified as correct with gauges and the upper receiver and bolt should work correctly together - generally not a selling point but more of a basic expectation.

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