Ok, here you go, but please bear with me as I am going from memory and the last time I handled an M240 was 1978....And I'm too lazy to go find the right book,
First off, with an open bolt system, ANY open bolt system, odds are the bolt will be forward after it runs dry. And this is because of the user, not the design.
In an open bolt system, yes, the bolt will remain to the rear after the shot, if the trigger is released.
IF the trigger is still held back on the last round, the bolt will go forward on an empty chamber. This is usually the first indication the shooter has that he is out of ammo. Full autos are like that.
Belt fed guns using the push through type links typically feed the belt on the rear ward movement of the bolt. The forward movement moves the feed pawl back to the "outside" position, so it snaps over the next round in the belt. The bolt going forward does this at the same time it strips the round out of the link, shoves it into the chamber and fires it.
The bolt coming back after firing extracts the fired case and ejects it, and advances the belt putting the next round into position to be fed into the chamber. The movement of the belt shoves out the empty link. If the trigger is held back, the cycle repeats automatically until the ammo runs out or the trigger is released.
If the bolt is on its way back when the trigger is released, it comes back, and is held there. If the bolt is on its way forward at the moment the trigger is released, it fires the round, and is caught and held when it comes back.
The position of the bolt when inserting the new belt is not important except that it is critical to the way you load the belt. You load the belt into the gun one way if the bolt is forward, and a differnt way if it is back. And if you use the wrong one, the gun will either not fire when the trigger is pulled, or jam when the bolt is pulled back.
There is a part of (or on) the feed tray called the cartridge stop. It sticks up, and "stops" the round from going past the position for feeding into the chamber. There is also a part, or parts known as "belt holding" or "retaining" pawls (they keep the belt from moving backward).
If the bolt is back, you load the belt with the first round up against the stop. Close the cover, pull the trigger and rock and roll.
If the bolt is forward, you load the belt with the first round just past the holding pawls, close the cover, and then pull the bolt back. This moves the first round into feeding position.
If you put the round all the way to the stop, with the bolt forward, pulling the bolt back will jam the gun. If you just hook the belt over the holding pawl(s) with the bolt BACK, sending the bolt forward will close it on an empty chamber.
This is a general description, common to a lot of guns. I'll have to look up a pic of the M240 parts to be certain, but I believe the 240 works this way, as well. When I do get able to check it out, I'll post a confirmation (or a denial
The military will have a set procedure, to load the gun the same way each time (helps cut down on mistakes). While you can get a gun running by loading either way, they will teach one way only, such as only loading with the bolt back (pulling it back if needed, before inserting the belt). Gunners will be trained to that standard. We were taught to pull the charging handle back if/when the gun quit. Then open the cover, and insert a new belt to the stop.
Hope this helps. Welcome to TFL!
andI'm going to move this to the full auto forum,