Smith & Wesson J Frame Mainspring/Hammer Spring All Models — Factory New Part 071040000

Smith & Wesson J Frame Mainspring/Hammer Spring — All Models, Factory New OEM Part

Genuine factory new Smith & Wesson OEM mainspring (hammer spring) for all J Frame revolvers. The mainspring is the powerplant of the fire control system — it provides the force that drives the hammer forward to strike the firing pin and ignite the primer. A worn or weakened mainspring causes light primer strikes, misfires, and inconsistent ignition. This factory replacement restores proper spring tension and reliable ignition to factory specification. Compatible with virtually all J Frame models from vintage to modern production, including both centerfire and rimfire variants.

Specifications

• Part Number: 071040000
• Manufacturer: Smith & Wesson
• Part Type: Mainspring (Hammer Spring)
• Material: Heat-treated spring steel
• Frame Compatibility: J Frame — all models
• Caliber Compatibility: Centerfire and rimfire J Frame models
• Condition: Factory New — genuine OEM part

Compatible Models

This mainspring fits all Smith & Wesson J Frame revolvers, including but not limited to:

30, 31, 32, 33, 34, 35, 36, 37, 38, 40, 42, 43, 49, 50, 51, 60, 63, 317, 331, 332, 337, 340, 342, 360, 431, 432, 437, 438, 442, 460, 631, 632, 637, 638, 640, 642, 649, 651, 940

Signs You Need a New Mainspring

• Light primer strikes or occasional misfires
• Inconsistent ignition, especially with hard primers or in cold weather
• Noticeably lighter trigger pull than when new
• Visible wear, corrosion, or damage to the spring
• Revolver has been in long-term storage

Important Notes

• This listing is for the mainspring only. The strain screw, hammer, and all other parts are sold separately.
• The mainspring must provide exactly the right tension — too weak causes misfires, too strong increases trigger pull weight. Always use the OEM factory spring for correct specification.
• Mainspring tension is adjusted by the strain screw at the bottom of the grip frame. Do not modify spring tension without understanding the effect on ignition reliability.
• Professional gunsmith installation recommended for proper fit and function.