I am certain that you could find a better lubricant for firearms usage than what is used in watchmaking. The temperature ranges and viscosity demands are quite different between the two. Both my grandfather and father were watchmakers for many years, so I do have experience with the oil that you mention. If I were to look for an alternative lubricant I would suggest starting with something like a chainsaw bar oil or bicycle chain oil. It is extremely weather and wear resistant with a high viscosity that is designed to bond to metal well and stay where it is put. My only concern would be the temperature resistance, provided you removed any excess from the barrel before loading and firing with a dry patch though I don't see why it wouldn't work well.