To the OP
If you would have described a common or even an obscure pistol a bunch of members would have given you more information than you would have wanted. What you described sounds like something custom. I agree with some of the other poster's who stated telling the caliber of a firearm pointed at you can be truly difficult. When you add in clip instead of magizine, stock instead of grip I honestly doubt your source truly knew the caliber as it's clear they don't understand pistols well.
Good luck with your research and if you do find this pistol please come back and teach us a little.