My father in law and I have been shooting his newly acquired 15-2 and had no problems until today. The cylinder became hard to rotate when it cycled to one chamber in particular after the first 6 shots fired. Then noticed the cartridge would not fully go into this chamber. Gun became impossible to fire when it got to this chamber by end of the 50 round box of ammo. Finally figured out that to get it to shoot when it cycled to this chamber had to start to cock the gun, then push the cylinder forward at the same time and this would allow cylinder to rotate and then could fully cock the gun and fire it. Needless to say this is not a confidence booster, especially to my father in law who just purchased gun and is (was) like a kid in a candy shop! Factory ammo used (winchester and remington 125 grain). Any ideas out there as to what is going on and how to fix this???