After extensive use in a cold climate, we would spray down the barrel and action with WD-40 and let it sweat it out over night. Then do a good clean the next day using CLP, leaving only a light coat of CLP on the firearm before it's put back in the vault.
BAD! It will cause your weapons to rust... For a quick clean, go down to the motor pool and get a can of "Blast off". They use it like a break cleaner, and will knock the carbon off quick. Then you can just coat it with good old CLP!
I will normally use blast off, and then a shit load of CLP. Allow it to sit over night, and then wipe it down the next day. The CLP will soak in to the metal, and when the weapon starts to get hot while firing. You will see the metal look wet, b/c the oil is reacting to he heat. I find that the less amount of CLP on the gun (while shooting) the better they work.
WD40 was never meant to be a lube or cleaner. WD stands for water displacement. The 40 was added because it was the 40th formula tried. Great for cleaning a distributer cap if you can still find a vehicle that has one but thats about it.