All manufacturing and all manufacturers require 'tolerances'. That is to say, there is some difference in measurements from one brand to another and from one lot to another. This includes both firearms and ammunition.
Most of the time it all works fairly well, once in a while one finds a firearm of 'minimum' size' and ammunition of 'maximum' size. Then it doesn't fit right.
Such is life.
I guess so... I just find it funny that American brands Never fit, but European ones Always fit
...... I suffer from a very rare genetic defect that causes me to be sympathetic toward the International cause. There is no cure.