What rounds you fire through your M16 rifle or M4/M4A1 carbine make a difference in barrel erosion. That’s why the Army is fielding a new bore erosion gage, NSN 5220-01-676-3452.
The new gage takes different measurements according to whether you’re primarily firing M855 or M855A1 rounds. Gaging to the specific ammunition being fired ensures accuracy.
WP 0026-5 of TM 9-1005-319-23&P (Apr 19) shows how to use the new gage.
Here’s how to use the gage:
- Install the key and bolt carrier with the bolt and firing pin removed.
- Hold the upper receiver with the receiver up.
- Insert the barrel erosion gage all the way into the rear of the upper receiver.
- The reject mark should be read at the rear surface of the upper receiver.
- If the reject mark passes beyond the rear surface, the barrel is NMC and should be replaced.
If the weapon has been primarily firing M855A1 rounds, use the M855A1 REJECT line on the gage. If the weapon has been firing M855 rounds, or if you’re not sure what rounds have been fired, use the M855 REJECT line.
Units need to order the gage with NSN 5220-01-676-3452. It will not be sent to the field automatically.
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