Several of the semi-automatic pistols in Receiver 2 can be loaded direct to chamber, that is; pulling and locking the slide back and placing a round directly into the chamber, namely;

• Beretta 92FS
  
• Colt 1911
  
• Desert Eagle Mark I
  
• Glock 17
  
• Sig Sauer P226 MK25

Why would you want to do this? Well two reasons, one: you may wish to have that one extra round loaded in an expedited fashion, rather than loading via the magazine only to have to remove the magazine to replace the one you racked. Two: you can deliberately reproduce a double-feed malfunction to practice your clearance drills.
The procedure is the same for the above firearms, with some subtle differences, but the basic actions are as follows, precondition; an unloaded firearm with no magazine inserted:

1. Pull back the slide with R, lock the slide in place with T, release R
   
2. Press Z to load a round direct to chamber
   
3. Release the slide with T

At this point the firearm is made ready and is live, you can now insert a fully loaded magazine and benefit from that extra round.

The process starts in a similar fashion to direct chamber loading, with an exception, assuming the precondition of an unloaded firearm with no magazine inserted;

1. Pull back the slide with R, lock the slide in place with T, release R
   
2. Press Z to load a round direct to chamber
   
3. With the slide still in the locked rear position, insert a loaded magazine
   
4. Attempt to release the slide

On attempting to release the slide, it will start to pick up a round from the magazine and stop against the round you previously loaded direct to chamber. From here you can practice your double-feed clearance drills.

This is already explained in-game, but for completeness sake with this guide I will give a basic actions-on for clearing a double-feed;

1. Hold back the slide with R and lock it back by holding T and releasing R
   
2. Release the magazine, the double-fed round should fall out

At that point you can either eject the round/casing that's still in the chamber, or leave the round there and release the slide** and load a fresh magazine.

**Releasing the slide at this point is important if you left a round chambered, because if you don't; loading another magazine will result in another double-feed malfunction.

Thank you for reading, have a happy double-feed clearing drill practice.