Carbine jams
If it inconsistent in operation, then I would suspect ammo or dirt. What ammunition are you using.....factory or reloads.
The Carbine operates on gas pressure. Field strip it, and under the barrel you will find a projection with a small captive piston in it. The piston should move freely, but it does need cleaning sometimes. There is a special wrench to remove the nut that holds it it, and you can probably find them on E-bay or war surplus parts dealers.
HINT: They would not have made the wrench and special brush to clean these if they thought a cleaning would not be necessary.
Also, put a bit of lubriplate or similar grease on the cam in the action slide (the cocking handle thingie). The right hand lug on the bolt rides in this slide groove, and the grease helps get things moving without friction. Do not put grease on the locking lugs themselves, only the outer end of the right hand one where it fits into the operating handle slide.
Clean out the inside of the body and action. Try different magazines. With the rifle unloaded, and no magazine in it, try cycling the action by hand using the operating (cocking) handle. Do it slowly to see if anything is binding.
Try testing with factory ammo after you clean it.
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