454 Raging Bull Questions

Hoping someone can help. I recently purchased a 454 RB and took it to the gun range this past weekend and had some issues with it. I put about 15 rds of Hornady 300gr JHP through it and then it stopped cycling the cylinder in SA and DA both. Has anyone had this same experience?

Also, I need to know if I can shoot the pistol off a sandbag with the barrel resting on the bag? Anyones help would be greatly appreciated.