Making Sear Springs

[smithy]

We have been making spring for some time but are still working to master these skills. We can use this thread to collaborate and learn.

Several steel types are commonly recommended due to their specific properties:

• 1075 Steel: This steel is often used for gun springs due to its medium carbon content (0.75% carbon), which offers a good balance of strength, ductility, and workability. It's easier to machine and heat-treat compared to some other high-carbon steels, making it suitable for small, intricate parts like sear springs.

• 1095 Steel: With a higher carbon content (0.95%), 1095 steel provides even higher elastic limits and fatigue strength, which are crucial for springs that need to maintain their shape and function under repeated stress. This steel can be hardened and tempered to achieve excellent spring properties but requires careful handling during heat treatment to avoid brittleness.

• 6150 Steel: This is an alloy steel containing chromium and vanadium, which further enhances its hardenability, strength, and resistance to wear. It's particularly noted for its toughness and is often used where high performance under stress is needed, although it might be less common for small parts like sear springs due to its complexity in processing.

• Music Wire (ASTM A228): While not primarily mentioned in gunsmithing contexts, music wire is a type of high-carbon spring steel known for its high yield strength and elasticity. It's used in various applications requiring spring-like properties but might be overkill for sear springs unless very specific elastic characteristics are needed.

The choice between these steels largely depends on:

• Durability and Fatigue Resistance: You want the spring to last through many cycles without failure.

• Elasticity: The spring should return to its original shape after being deformed.

• Machinability: For intricate shapes like sear springs, how easily the steel can be cut, bent, or shaped is important.

• Heat Treatability: The ability to achieve desired hardness and toughness through heat treatment.

For a sear spring, where precision and reliability are paramount, 1075 steel often stands out due to its ease of use and good performance characteristics. However, 1095 might be preferred if the highest possible strength and elasticity are required, although it requires more careful handling during manufacturing.

Therefore, for most applications, 1075 or 1095 steel could be considered optimal, with the choice depending on the specific demands of the firearm and the manufacturer's capability in heat treatment and machining.

[smithy]

Determining the optimal thickness for a sear spring made from 1095 steel involves balancing several factors:

• Spring Rate: This is how much force is required to compress or extend the spring by a given distance. Thicker steel will generally result in a stiffer spring.

• Durability: Thicker material can handle more stress and last longer, but it also increases the load on other parts of the firearm.

• Geometry and Space: The physical constraints of where the spring fits in the firearm dictate a maximum thickness.

• Functionality: The spring must provide enough force to ensure the sear engages properly but not so much that it causes overly high trigger pull weights or wear on other components.

For a typical sear spring:

• Common Thickness: Sear springs are often made from material with a thickness of about 0.015" to 0.020" (0.38mm to 0.51mm). This range is typical because it provides a good balance between spring strength, durability, and the space constraints within the firearm.

• Precision: The exact thickness might be slightly adjusted depending on the specific design of the firearm, the desired trigger pull weight, and how the spring is formed (flat springs vs. wire springs). For custom or precision work, thicknesses might be fine-tuned, but they rarely go much above 0.025" or below 0.010".

• Testing and Iteration: In practice, gunsmiths or designers might prototype with different thicknesses to see which offers the best performance, adjusting based on actual firing tests for trigger pull, reliability, and longevity.
  Material Properties: Since 1095 steel can be hardened significantly, even at these thin gauges, it will maintain its shape and function well under repeated stress, provided it's properly heat-treated.

Therefore, for an optimal sear spring made of 1095 steel, consider starting with 0.018" (0.46mm) thickness as a middle ground, then adjust based on practical testing and the specific firearm's needs. Remember, the final choice will depend on how the spring interacts with other parts of the gun, so empirical testing is crucial.

[smithy]

When choosing between hot-rolled and cold-rolled 1095 steel for making a sear spring, several factors come into play:

Cold-Rolled 1095 Steel

Advantages:

• Better Surface Finish: Cold-rolled steel typically has a smoother, more uniform surface which can be advantageous for small, precise parts like sear springs.

• Tighter Tolerances: The cold-rolling process can achieve more precise dimensions, which is beneficial for consistency in spring performance.

• Increased Strength: The work hardening from cold rolling can increase the steel's hardness and tensile strength before heat treatment.

Disadvantages:

• Less Ductility: Cold-rolled steel can be less ductile due to work hardening, which might complicate forming operations if not managed carefully during heat treatment.

Hot-Rolled 1095 Steel

Advantages:

• Greater Ductility: Hot-rolled steel tends to be more ductile, which can be advantageous when forming complex shapes like springs.

• Potential Cost Savings: Generally, hot-rolled steel can be less expensive than cold-rolled due to simpler processing.
  Disadvantages:

• Surface Imperfections: Hot-rolling might leave scale or surface irregularities that need to be cleaned or removed for precision parts.

• Less Precise Dimensions: Hot-rolled steel might not have the same dimensional accuracy as cold-rolled, potentially leading to more variability in spring performance.

For Making a Sear Spring:

• Precision and Surface Quality: Given the need for precision in sear springs, cold-rolled 1095 steel would generally be preferred. The smoother surface and tighter tolerances are critical for consistent spring performance and to ensure that the spring fits perfectly in the firearm's mechanism.

• Heat Treatment Considerations: Both can be heat-treated to achieve the necessary spring properties, but cold-rolled steel might require less work to get to the final desired properties due to its pre-existing hardness.

• Forming: If the spring design involves complex shapes or bending, you might need to consider the initial ductility. However, with proper heat treatment (annealing before forming and then hardening/tempering), cold-rolled steel can be made to work well for these applications.

Conclusion: Cold-rolled 1095 steel is typically better for making sear springs because of its superior surface quality, dimensional accuracy, and initial material properties. However, the choice can also depend on your manufacturing capabilities, the specific design of the spring, and whether you're willing to invest in the additional steps to prepare hot-rolled steel for use. If cost or availability is a significant concern, hot-rolled might be used with additional processing to achieve similar results.

[smithy]

Process:

1. Ready the required components.

searspring1.png (386.34 KiB) Viewed 69 times

2. Sear springs typically have a small tab that inserts into the lock. I find it easiest to cut/file the tab prior to making any bends.

3. Optional: Build a jig to help ensure the proper dimensions. I can make these springs without but found that using a jig for the initial heat and bend helps.

searspringjig.png (430.65 KiB) Viewed 69 times

4. Heat the metal until just glowing orange in addition to carefully heating the pliers or other tool you are going to use to grab and bend the metal.
5. Bend the metal to the rough shape and dimensions
6. Optional: Remove from jig
7. Continue to heat and work the spring into the desired shape.
8. Let cool at room temperature. I do not cool with any liquid at this point.
9. Test the fit and file as needed.
10. Carefully heat the spring trying not to overheat until the spring is no longer magnetic and quench in oil
11. Let fully cool and lightly sand the spring to return it's bright raw fishing.

searspring3.png (327.91 KiB) Viewed 69 times

12. Temper the spring in the appropriate areas until they are blue.
13. Cool and slowly work it to break-in the spring.
14. Mount and test spring.

searspring4.png (510.67 KiB) Viewed 69 times