Back then an abdominal injury from a gunshot or any other penetrating object was pretty much a death sentence. A pine box was the only treatment they had. Even if the doctor had the surgical technique to go in and repair the damaged tissue which they didn't, there were no surgical sterile methods back then, and there were no antibiotics to protect the patients from the inevitable bacterial infection that would have resulted from the injury and the surgical procedure. Bacteria is everywhere. It the wound was superficial then the patient had a chance to survive, but if the bullet pierced the peritoneum the odds of survival were extremely low. Especially if the penetrating object perforated an internal structure or organ.
Gut shot civil war time one big worry was infection. Not the cleanest conditions were available. Most limbs were removed because it was easier and faster. So many injuries some battles they had little or no time