I took a brand new GP100 357 mag to the range and second shot locked up the cylinder. Problem wasn't the gun, but rather an improperly seated factory round (major manufacturer). The range officer wouldn't let me fix the problem, nor would he allow me to bag the gun with hammer locked back. Fortunately, the range gunsmith came to my aid and fixed the problem (less than two minutes) at no charge. I've never had another problem with the gun or any ammo.