More to the point, It's German training ammo for the G3 rifle.
It won't cycle an M14 and there is no way to safely get it to do so.
The G3 battle rifle uses this ammo with a special bolt that is lighter and has less resistance to get it to cycle.
There is no way to do this on an M14 since it's a gas operated action. The 10 grain plastic bullet leaves the barrel without building up any gas pressure.
You just have to shut off the spindle valve on the gas system and yank the op rod back each time.