Are you sure they are FMJ and not plated? I've experienced that before with plated bullets, especially in 10mm and the Glock bore. The plated stuff is generally too soft to grip Glock rifling at higher speed and pressure, where normal bullet jackets work fine.
I guess I'm not sure about that, but thanks for the info. Polygonal rifling issue, I guess? I sold the rest of that lot to a guy who will be shooting them in a 1911, so hope he has better results.