I've seen a few old Winchesters where the frame have peeled back like a banana, all were due to double charge of a fast burning powder. Looking at the pics; my guess is, that is what happened here. From the way the barrel is fractured, looks like a detonation.

The barrel steel also has me curious, it looks fractured, very little bulging or stretching. Generally you don't see that with Winchester barrels, or barrels made of proper barrel steels such as 12L14 or 4140. I don't know of anyone using Stressproof 1144 for barrels.

Mike Hunter
Hunter Restorations

Mike Hunter
www.mikehunterrestorations.com