NEWS | Aug. 12, 2021

M249 Machine Gun: Won't Fire? Check Piston Pin

This article initially appeared in PS 758 (May 16), p. 42. 

Dear Editor,

Recently I was trying to repair an M249 that wouldn’t fire. It would chamber rounds and extract them with no problem when I worked the weapon manually with dummy rounds. But when I had Soldiers test fire it with blanks, it still wouldn’t fire. I did the normal troubleshooting, but nothing turned up.

Then I checked the unfired blank round and discovered that it didn’t have the normal deep mark on its primer from the firing pin strike. That led me to check the gas piston. I found its roll pin was broken and the gas piston was sticking out too far.
Won't fire? Check roll pin
Won't fire? Check roll pin

Once I replaced the pin, the M249 fired great.

Small arms repairmen might want to keep this in mind when they can’t figure out why an M249 won’t fire.

Scott Taylor
Ft Benning, GA
Editor’s note: Excellent tip, Scott! Thanks for pinning down that problem.