The mainspring in this lock appears to be from a Dixie F1, or P1 lock, and is a bit too short, as Bob mentioned. These springs were very strong, and can fracture the stock if they unload in the lock mortise. The lock bolt is causing the spring to flex primarily out on its end instead of throughout the lower arm, which can lead to breakage.
Before you attempt to shoot this gun, I would inspect the breech. It appears to be a patent breach, with the touch hole bored way far forward. This could mean that the touch hole is bored out beyond the breech threads, rather than through the plug and into the powder chamber. This is why the lock is so far forward in the stock, I suspect.
With all these issues, I would completely disassemble this gun, and inspect it, before firing it.
Hungry Horse