Apples and oranges
Snakes M10 was an open bolt semi auto, unmodified. No stock, no selector, semi auto only. It can be seen firing semi auto in the scene where the duke is using the president for target practice. The “full auto” scenes were most likely filmed the same way that they did with Scarface and many other movies, using a semi auto rate of fire, firing somewhat rapidly, with full auto sounds dubbed in over it. The reason they do this has something to do with the speed of the camera, the semi auto shots are timed better with the camera shutter allowing it to pick up more of a visible muzzle flash. I read a write up about how they did it with Scarface during the final shootout with Tony and his M16, despite the gun being a true selective fire variant, they opted for the semi auto selection to get more of the muzzle flash on camera and then overdubbed it with full auto sound FX. In EFNY, snake is seen shooting “full auto” on a couple occasions, but the sound of the gun that they dubbed is a very fake movie silencer type of gunfire noise. The scene where the Duke is shooting semi auto at the president was live fire, and seems to be the genuine sound of the gun with no overdubbing. That scene also shows us that the suppressor on the gun is a fake suppressor, as it has no sound suppression qualities whatsoever.Plissken’s M10 looks in every picture/vid to be devoid of a selector switch or sear pin hole. Probably a modified open-bolt semi by a prop house.