{"product_id":"smith-wesson-j-frame-mainspring-hammer-spring-all-models-071040000","title":"Smith \u0026 Wesson J Frame Mainspring\/Hammer Spring All Models — Factory New Part 071040000","description":"\u003ch2\u003eSmith \u0026amp; Wesson J Frame Mainspring\/Hammer Spring — All Models, Factory New OEM Part\u003c\/h2\u003e\n\u003cp\u003eGenuine factory new Smith \u0026amp; 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.\u003c\/p\u003e\n\u003ch3\u003eSpecifications\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003ePart Number:\u003c\/strong\u003e 071040000\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eManufacturer:\u003c\/strong\u003e Smith \u0026amp; Wesson\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePart Type:\u003c\/strong\u003e Mainspring (Hammer Spring)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMaterial:\u003c\/strong\u003e Heat-treated spring steel\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFrame Compatibility:\u003c\/strong\u003e J Frame — all models\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCaliber Compatibility:\u003c\/strong\u003e Centerfire and rimfire J Frame models\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCondition:\u003c\/strong\u003e Factory New — genuine OEM part\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eCompatible Models\u003c\/h3\u003e\n\u003cp\u003eThis mainspring fits all Smith \u0026amp; Wesson J Frame revolvers, including but not limited to:\u003c\/p\u003e\n\u003cp\u003e30, 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\u003c\/p\u003e\n\u003ch3\u003eSigns You Need a New Mainspring\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eLight primer strikes or occasional misfires\u003c\/li\u003e\n\u003cli\u003eInconsistent ignition, especially with hard primers or in cold weather\u003c\/li\u003e\n\u003cli\u003eNoticeably lighter trigger pull than when new\u003c\/li\u003e\n\u003cli\u003eVisible wear, corrosion, or damage to the spring\u003c\/li\u003e\n\u003cli\u003eRevolver has been in long-term storage\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eImportant Notes\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eThis listing is for the mainspring only.\u003c\/strong\u003e The strain screw, hammer, and all other parts are sold separately.\u003c\/li\u003e\n\u003cli\u003eThe 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.\u003c\/li\u003e\n\u003cli\u003eMainspring 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.\u003c\/li\u003e\n\u003cli\u003eProfessional gunsmith installation recommended for proper fit and function.\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"Smith \u0026 Wesson","offers":[{"title":"Default Title","offer_id":32276867018,"sku":"071040000","price":11.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1423\/2020\/products\/24_12_f9a8982c-67ea-48f9-92c6-59e1e70cfb53.jpg?v=1637687303","url":"https:\/\/usagunsandgear.com\/products\/smith-wesson-j-frame-mainspring-hammer-spring-all-models-071040000","provider":"USA Guns And Gear","version":"1.0","type":"link"}