I'd add to this that he may be lying to himself first and foremost! The late (and great) physicist Richard Feynman said "the first principle is that you must not fool yourself...and that you are the easiest person to fool." I know a guy who tells me with all the sincerity in the world that his handloads in 270 wsm spit a 140 grain bullet at 3800 FPS with no pressure signs out of a 22 inch barrel (and there's barely and kick to boot, too good to be true huh?). In this case he's not lying in a deliberate, deceptive way so much as just hopelessly wrong and unwilling to consider as much. It could well be that this guy the OP is talking about isn't a liar in that he really does believe the things he's saying, even if no one else does. I know lots of people like this, good people who know things that "just ain't so" haha.