The old movie paid some attention to details. As you can see, his left hand pushed the barrel back in pix #6, this step unlocked the bolt, so he could use his right thumb to push back the bolt in pix #7. Without previous step, it's impossible to open the bolt with single thumb. The right thumb controls the bolt position -- not too far so it would not be locked by the follower, but opened big enough so the cartridge could be inserted. From pix #4 to #8, it took him 2 seconds. With practice, this can be repeated so 10 rounds could be loaded into the magazine without clip. Try it. Not easy at the beginning. I have also seen people could rotate this gun on finger like cowboy rotating a revolver. I could not do it no matter how many times I tried
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If you do try it, use snap caps. Don't play with live ammo.