What is this noise?

[pwrstrkd]

I dont know how I noticed this but on my m1a when the bolt is held open I can hear something sliding slightly back and forth when I tilt the gun foward then backwards. Does anyone know what is moving back and forth. I dont notice it when the bolt is closed however.

 

[zoomie]

Firing pin?

 

[AK103K]

Its the gas piston.

 

[pwrstrkd]

dumb question, but why cant i hear it when bolt is closed?

 

[AK103K]

The op rod is against it. When the gun is fired, the piston drives the op rod rearward.

If you take the barreled action out of the stock, you can see whats going on.

 

[James K]

If you can't hear that piston moving, it is time to clean the rifle.

Jim