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A broken mainspring on old guns it's a pretty common problem. Let me show you how to make a new one. This is a Marlin Ballard number two sporting rifle in 32 long. It was made in the 1880s. The bore is nice and bright, and it can still be shot with obsolete 32 rimfire ammunition, if you can find it.
Sometimes it misfires because the hammer doesn't hit the firing pin with enough force as the mainspring is weak. Another issue is the hammer won't hold in the half-cock notch. This is where the phrase "going off half-cocked" came from, as pulling the trigger may cause the hammer to fall when the hammer is in the safety, or half-cock notch. I'll need to remove the breech block to take a look. It's held in by a single screw.
Next, the extractor is removed, and the breech block and lever are slipped from the receiver. The breech block is constructed of two halves which are held together by several screws. After each screw is removed, I push it into a piece of cardboard to ensure it goes back in the same location it came from. With all the screws removed, I tap the halves apart. One interesting feature of the Marlin Ballard is the ability to switch the firing pin from rimfire to centerfire. Although extremely rare today, 32 Ballard centerfire ammunition was available when this gun was produced. With the breech block split apart, it's easy to see this mainspring isn't original to the gun, as it's a different color and brightness. Its design evolved from a V-type spring seen in earlier guns. The firing pin also changed. Early Ballards were rimfire only and the firing pin was an integral part of the hammer. One design remained fairly constant: the trigger return spring.
The original mainspring isn't arched as much as the replacement and the original has a round boss on the front to minimize friction where the tip of the spring contacts the hammer. It's pretty simple to make a new spring from standard spring steel stock. The stock comes annealed or soft and will need to be heat-treated to make it into a spring. I've selected a piece as thick as the ends of the original mainspring, although it will need to be thinned in the middle.
After cutting the new spring just slightly longer than the original, I coat it with DYKEM to show my marks more easily. The proper width is marked, and I file to the line. Keeping the line even with the top of the vise jaws makes filing easier.
Next, the end of the spring is filed to shape. This raised portion helps hold the back end of the spring in place. By holding the springs back-to-back, I can determine the correct length. The circular boss at the tip is filed and the spring is tapered from the tip to the back end.
Now we need to polish it lengthwise to remove all the file marks. I begin with 220 grit and finish with 320. Any scratches running across the spring could cause it to break at that point.
The last step in shaping the new spring is bending it to shape. I'm using the original spring as a pattern. The soft metal bends easily on a spring this thin.
To heat treat the spring, I carefully heat it to an even cherry red color, which is about 1400 degrees. Once the color is uniform throughout the part, it's quickly dunked in quenching oil, which leaves the steel extremely hard but brittle.
To remove this brittleness and turn the metal into a spring, it needs to be tempered, which is the second step of the heat-treating process. Tempering removes most of the brittleness and allows the steel to flex. I polish the spring bright, then place it in a pot of melted Nitre bluing salts. The pot temperature is about 600 degrees. Reheating the steel to this temperature removes most of the brittleness and the Nitre bluing salts give the spring an attractive blue finish.
Rinsing the spring in water finishes the heat-treating process and now the steel has its spring. I install the spring back into the breech block followed by the hammer and trigger. With the newly made spring in place, the hammer can't be bumped forward out of the half-cock notch, but the notch in the hammer is not quite deep enough to retain the nose of the trigger and prevent the trigger from being pulled. Not a problem -- it's a simple matter to cut the notch slightly deeper. Now there's a square recess in the half-cock notch to capture the nose of the trigger.
With the breech block reassembled, the trigger can't be pulled when the hammer is in the half-cocked position. There's one more issue I'd like to fix. At some point, it looks like this gun was dropped, damaging the muzzle. It's a simple matter to recrown the barrel. I begin by removing the forend. The serial number on the barrel matches the receiver, which is typical on 19th century guns. Next, the buttplate plate is removed. The buttstock is held on by a draw bolt. Again, the serial number is clearly evident. Last, I remove the sights, drifting them from left to right. The barreled receiver is fixtured in the lathe using a plug gauge to level the bore.
I make several light cuts along the muzzle until the damage is removed.
The outside edge of the barrel is chamfered by reversing the rotation of the lathe to cut on the backside of the barrel. The last step is to remove the slight burr at the edge of the bore. Fine abrasive on a brass lap bevels the edge and removes the burr.
The face of the muzzle could be browned to match the rest of the rifle, but I'm going to leave it bright for now. I reassemble the rifle and check the function one more time.
--Larry Potterfield
