S&W K Frame M&P 1st Model 4-Screw Strain Screw .38 Colt – Part# MPC9

Smith & Wesson K Frame Military & Police 1st Model Strain Screw – 4-Screw, Old Style

A rare factory-original strain screw for the earliest production K Frame revolvers. This part was sourced from a Military & Police 1st Model revolver (Serial# 3312) chambered in .38 Colt — one of the earliest S&W hand ejector revolvers ever produced. The strain screw threads into the grip frame and controls the tension on the mainspring — adjusting it affects trigger pull weight in both single and double action. Correct-era parts for these early 4-screw revolvers are extremely difficult to find.

• Part Number: MPC9
• Fits: Smith & Wesson K Frame Military & Police 1st Model (4-Screw)
• Caliber: .38 Colt
• Part Type: Strain Screw
• Era: 4-Screw, Old Style
• Finish: Blue Steel
• Provenance: Sourced from Serial# 3312
• Condition: Used (factory original)
• Installation: Gunsmith fitting recommended

Strain Screw & Trigger Pull

The strain screw is one of the few user-adjustable components on a S&W revolver. Backing it out slightly reduces mainspring tension and lightens the trigger pull — however, this can also cause light primer strikes. Always verify reliable ignition after any adjustment. Gunsmith guidance is recommended, particularly on these early revolvers where parts tolerances differ from later production.

Factory Replacement Quality

Genuine Smith & Wesson factory part from the correct production era — same thread pitch, same dimensions, same reliable mainspring tension control. Correct-era parts for these early revolvers are increasingly scarce.

About the M&P 1st Model

The Military & Police 1st Model (introduced circa 1899) was one of the first S&W swing-out cylinder revolvers and the direct ancestor of the legendary Model 10. Early production revolvers like Serial# 3312 predate the model number system by decades — if you're unsure whether this part fits your specific revolver, contact us with your serial number and we'll help confirm compatibility.

Questions? Call or email us — we're happy to help you get the right part the first time.