You could have to much end play in the bolt this can brake the pin.If you have movement take the pin and bend it in the center.It will draw the bolt back and you will be OK.
I would like to see any one try to install the barrels if you are not a gun smith.It is not for any home repairs.The gun plate was not made by smith.It could have been made on the out side and put on.Could you tell us the name on the bottom of the letter.
Can you please tell me why do want to spin your cylinder like you are!
By spinning the cylinder with the trigger back and your finger slips you will rip your stop notch up and have a hell of a burr on it.I replace more cylinders because of this.
I have in my paper-629-3 in1990/longer stop notch/added bolt block/fixed hand.
629-4 in 1993new style sight leaf / drilled&tapped frame.Hope this will help out.