Depends on the model
Screws?There are no screws on an AR15 bolt, a pin secures the assembly
First do a full functional clear, eject the mag, rack the bolt/carrier to eject any casing. Next fully clean the gun. Check for broken or weak parts in bolt/carrier, gas system, and buffer system. Use quality ammo. If it still doesn't then take the gun to someone who knows how to work on ar15 rifles.
The bolt carrier would not return, another round would be chambered, and you'd likely have to replace a bolt carrier, buffer tube, buttstock (if using a fixed buttstock), and buffer spring (if the spring was in the extension tube). You could also cause injury to yourself if the bolt carrier ended up going through the back of the extension tube.
Into the left side of the receiver.
The serial number and possibly on the bolt.
In firearms such as the AR 15, the bolt rides in a part known as the bolt carrier.
The bolt carrier, the firing pin, the carrier pin, the extractor, the cam pin, the bolt, the extractor retaining pin.... that's the assembly, but the charging handle is also defined as part of the bolt carrier group.
Depends on the rifle- some do not HAVE a bolt catch. On the AR15 family of rifles, it is the left side of the receiver.
It is a harder metal, and if the coating isn't done right, and excessive coating is put on, it can cause malfunctions... AR rifles have very tight tolerances, and aren't forgiving of things such as that.
ejector also
On the full auto carrier (Left) the channel on the bottom of the carrier that the sear trip lever rides in is closed on the rear end - on a semi auto bolt carrier (Right) the channel is cut all the way through.
The M16 assault rifle's bolt and bolt carrier are made of steel.