Colt made derringers from about 1870 to 1890, after buying out Brooklyn's National Arms Co. for their derringer designs. Sources disagree on the total numbers produced, but it is estimated that about 6,500 of them were made. The barrel pivots open to load and close to fire the .41 rimfire cartridges.
This old Colt #2 came into the shop completely rusted shut and non functioning. It had been found buried in the dirt floor of a barn. After a soak in solvent, I was able to get the gun apart. Ordinarily I would not recommend trying to restore a firearm that has honest patina, because you can reduce the value by half. But in this case, the poor gun didn't have much value due to the condition.
After getting the gun apart, I was able to,soak the parts in phosphoric acid to remove as much of the rust as possible. Then a good scrubbing with a wire brush took off the rest of the corrosion. I made no attempt to fill in or buff out the rust pits, and I left the remainder of the heavier patina on the metal surface.
There was some question of whether or not to add a finish to the old gun, and since the customer requested it, I opted for a thin coating of cold blue. Oxpho-blue from Brownells seems to give a good finish without blotching.
I turned my attention next towards making new springs. The trigger return and hammer mainspring were broken. I cranked up my gas forge and began bending the strips of metal to shape.
Matching the spring stock to the original shape.
Using an oxyacetylene torch and Kasenit, I was able to harden the spring. At this point, the spring is very hard and brittle.
Quenching the spring in oil.
I draw back the temper of my springs using a bullet casting pot of molten lead. It seems to work great, and never allows the metal to get hot enough to lose the "springiness".
The new springs are in the gun. I draw the hammer and release it numerous times to check and make sure the springs don't crack. When polishing the springs before heat treating and tempering, I always make sure to polish them lengthwise and never across them. Any scratches that don't go the length of the springs will form micro fissures and the springs will crack at those points.
At this point the pistol has been restored to functional condition. All that's left remaining to do is make some .41 rimfire ammunition and test fire this pistol.