There should not be any so far as reliability goes. Any gun will smooth up after use, but we should stop accepting failures in brand new guns because someone says they need "broken in".
By some strange coincidence, when the gun still fails after the "break in" period (and most will), it is now a used gun and out of warranty.
(Do not confuse a break in period with a test run to ensure that the gun works with the ammo you want to use. Not the same thing.)
Jim