If you’ve been fighting a heavy double-action pull on your S&W N-Frame or X-Frame revolver, the Mass Driver Hammer is a direct swap that lets you lighten the trigger without losing reliability. This component replaces the factory MIM hammer, sear, stirrup, and spring with a heavier forged-steel hammer that puts more mass behind the firing pin strike. The extra mass means you can reduce the hammer fall weight and still get consistent ignition—whether you’re shooting rimfire 22s or centerfire loads. It keeps the single-action feature intact, so you don’t lose that crisp SA break you’re used to.
Will This Fit My Gun?
This kit is designed for current-production S&W N-Frame and X-Frame revolvers with a frame-mounted firing pin (you’ll need to remove the side plate to access it). It will not work on K, L, or J-Frame models.
- S&W Model 25
- S&W Model 27
- S&W Model 29
- S&W Model 57
- S&W M&P R8
- S&W 325, 327, 329, 329PD
- S&W 350
- S&W 500
- S&W 610, 625, 627, 629, 929
- S&W Governor
Key Features
- Heavier hammer mass improves ignition with rimfire and centerfire ammunition
- Allows a lighter double-action trigger pull than stock MIM parts
- Maintains single-action function
- Replaces factory hammer, sear, stirrup, and spring for consistent performance
- Made in the USA (Phoenix, Arizona)
Install Difficulty
Difficulty: 3 out of 5 – Intermediate. You’ll need a good set of gunsmith screwdrivers (hollow-ground, not tapered), a small punch, and a non-marring hammer. We recommend watching our install video before starting. If you’re not comfortable removing the side plate and swapping hammer components, have a qualified gunsmith do it.
Frequently Asked Questions
Will this work with my S&W 629?
Yes, the 629 is an N-Frame model and is compatible with this kit. Just make sure your revolver has a frame-mounted firing pin (not on the hammer).
Do I need to change anything else to get a lighter pull?
This kit alone will let you lower the hammer fall weight, but you may also want to install a lighter trigger return spring for further pull-weight reduction. Many shooters pair this hammer with a reduced-power mainspring.
Does it retain the factory single-action feel?
Yes. The Mass Driver Hammer keeps the single-action sear engagement point, so you’ll still have that clean SA break you expect from an N-Frame. The improvement is in the double-action pull.
Shipping & Warranty: We ship within one business day, and this kit comes with a limited lifetime warranty against defects in materials or workmanship. If you have any fitment questions, give us a call—we’re happy to help.
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