What you do to the slide with your hand is not the same as what expanding gasses do to it. There's a difference in both force and timing.
Somehow get the first cartridge into the chamber, and then fire the thing. Shoot a magazine-full. I bet it works OK.
Time and use will slick-up the pistol's innards.
If you don't want to wait for that to happen, then polish the feed ramp, barrel hood, and chamber so that the first cartridge feeds easily.
(Do not use a power tool for this job. If you want instructions, PM me.)