Mass Driver Hammer for S&W N-Frame Revolvers

This kit replaces the factory MIM hammer assembly in S&W N-Frame and X-Frame revolvers with a heavier mass driver design. The increased mass behind the hammer face allows the shooter to run a lighter mainspring (reduced hammer fall weight) while maintaining reliable ignition across both rimfire and centerfire ammunition. The primary problem this solves: you can lower double-action pull weight without inducing light strikes on harder primers. The sear, stirrup, and spring are included as matched components to ensure consistent lock time and trigger reset.

Compatibility

• Smith & Wesson N-Frame: Models 25, 27, 29, 57, M&P R8, 325, 327, 329, 329PD, 350, 610, 625, 627, 629, 929
• Smith & Wesson X-Frame: Model 500, Governor
• Requires frame-mounted firing pin (accessible only with side plate removed)
• NOT compatible with K, L, or J-Frame revolvers
• Fits current production N/X-frame models only

Key Features

• Increased hammer mass improves primer strike energy without increasing mainspring tension
• Allows reduced double-action trigger pull weight while maintaining ignition reliability
• Maintains single-action functionality
• Replaces factory MIM hammer, sear, stirrup, and spring with billet/bar stock components
• Manufactured in Phoenix, AZ (USA)

Install Difficulty: 3/5

Requires side plate removal, mainspring replacement, and hammer/sear timing adjustment. Tools needed: gunsmith screwdrivers (hollow-ground), roll pin punch set, brass hammer, mainspring winder tool. Recommended for experienced revolver armorers. Spring weight tuning may be required for specific ammunition types.

FAQ

Will this work with my Model 686 or Model 66?

No. This hammer is designed exclusively for N-Frame and X-Frame revolvers. It will not fit K, L, or J-Frame models due to frame geometry differences.

Can I use this with a reduced-power mainspring?

Yes—that is the intended use. The mass driver design compensates for lighter mainspring tension by increasing hammer momentum. Start with the kit’s supplied spring and tune down if ignition remains consistent.

Does this require professional installation?

Strongly recommended unless you have revolver timing experience. The sear engagement and stirrup orientation must be set correctly to maintain safe single-action operation. Improper installation can cause misfires or hammer follow.

Ships same business day if ordered before 2 PM EST. Limited lifetime warranty against manufacturing defects. Installation errors not covered.