FTF, root cause

If I am having a failure to feed, (the round is partially pushed in, just not all the way). What is the root cause? Is it more of a Bolt, carrier or what?

A friend let me use a Young BCG, heavier version. The Bolt felt a little tight? It looked like a regular Bolt with Young carrier.

16 inch carbine, nothing special.

pb

Did it do this with one mag or with other mags too?

Is the round making it into the chamber but the bolt is not locking? What ammo? What barrel?

The round would be half way in the chamber.

I used my LMT enhanced Bolt today and the problem went away completely. 300 rounds, Probably 150 with that BCG / gun. I was going to try one of my Colt Bolts but just got this LMT so I wanted to try it. My guess is the Colt Bolt would have solved the problem as well.

The gun was a Colt 6940. Was using Rem Green box. Used Silver Bear 62 grain ammo today. Maybe the Silver Bear solved my problem. ?