He released the slide but the bullet hadn't managed to eject, so the bullet was jammed halfway out between the slide and the frame, leaving the slide out of battery and the gun useless. This is what happened: when he racked the slide this time his fingers must have been blocking the ejection port again, so when the slide retracted the bullet didn't have enough space to escape the chamber. See it coming away from the gun? He's just used it to rack the slide, but he wasn't paying attention - no close camera shot of the gun this time, he wasn't even looking at it. Now watch when Ocelot tries the same again on Snake. In fact it looks like the cartridge was forced to eject backwards out of the port because Ocelot's hand was blocking it - if Ocelot hadn't covered the port at all the bullet would have jumped much more sideways to the right and upwards instead of backwards behind the gun. When he racks the slide, he totally covers the ejection port with his fingers, just leaving enough of a gap for the ejected cartridge to escape. Watch the first time he quickdraws, on the KGB guards. No, what you've missed is the catalyst - Ocelot did exactly the same thing twice (round in chamber, new mag in and shoot) but it didn't work the second time. Unless Makarovs can't eject unfired cartridges, which seems unlikely. The bullet from the magazine would only chamber when the slide is retracted, at which time the bullet in the chamber would be ejected.

Since there was already a bullet in the chamber, the first bullet from the magazine couldn't be chambered, and was therefore jammed between the loading part of the chamber and the the already chambered bullet Since there was already a bullet in the chamber, the first bullet from the magazine couldn't be chambered, and was therefore jammed between the loading part of the chamber and the the already chambered bullet, which caught Ocelot completely off guard. When he loaded a new magazine, he forgot to cock the slide back because he didn't think that there was already a bullet in the chamber. Before he arrived at the site with Snake and KGB guards, he had already loaded that new magazine, so he took out the pistol, cocked the slide back, ejecting the first bullet (which was from the previous magazine), and took out the guards. Just keep in mind that the Makarov carries eight rounds in each magazine, but Ocelot kept the final bullet from the last magazine chambered in the pistol, before loading another new magazine. Snake's is probably the simplest explanation, concerning the gun jam. The only techniques you can rely on are the ones you've mastered through experience and practice. And he was obviously motivated by vanity to show off his new technique. in any case, he probably wanted to try it out for himself. He must have heard about it from someone, or read it somewhere. By making sure there's always a round in the chamber, you eliminate the risk of pulling the trigger with nothing to fire. It's a technique they teach in the Middle East. Whenever he put a new clip in his gun he'd always load the first round by hand, whether there was a round left in the chamber or not. Copied from an old gamefaqs post by mookiethebold

Mgs3 ocelot gun jam