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Sig Sauer® P320™ Lower Parts Kit - 9mm/.40/.357



If you're building a Sig Sauer® P320 compatible sidearm, then you need a lower parts kit to complete your MUP-1. That's the part legally considered the firearm, which means it's the part upon which you change out frames, slides, etc., to convert the pistol to the various other P320 sizes. This lower parts kit is the correct one to finish the job. It comes with all the parts needed to make your 9mm, .40, or .357 chambered MUP-1 fully functional. See below for more info.

Please note: This LPK will not work on builds chambered in an actual Sig Sauer® P320 chambered in .45acp or a P320 compatible 80% build chambered in .45acp.

What's Included:

  • Lightweight Adverse Trigger
  • Sear Housing
  • Sear
  • Safety Lever
  • Trigger Bar
  • Takedown Safety Lever
  • Takedown Lever with O-Ring
  • Mechanical Disconnector
  • Trigger Bar Spring
  • Sear Spring X2
  • Takedown Safety Lever Spring
  • Sear Housing Pin
  • Trigger Bar Stop Pin
  • Sear Pin
  • Slide Catch Lever Pin
  • Safety Lever Pivot Pin


WARNING: Handling firearms parts and accessories can expose you to lead and other petroleum products known to the State of California to cause cancer and reproductive harm. For more information go to: www.P65Warnings.ca.gov

Made in the USA  Lifetime Warranty

Shipping Restrictions

Shipping of various parts and/or accessories are prohibited to states and locales (ie New Jersey, California, New York, etc…) with restrictions against certain parts and/or accessories or “assault weapons” (i.e. states with high-capacity magazine restrictions, manufacturing of semi-automatic weapons, etc..). It is your responsibility to be aware of your local firearms laws before purchasing from our website or machining a firearm. We try our best to keep our shipping page current, but laws change daily

80LowerJig.com only ships within the United States. Federal legislation dictates we cannot ship our products internationally.

We are a national retailer of individual components and not all products depicted on this website are legal in every state. Shipping of various products found on this website are prohibited to some states (such as California, Connecticut, District of Columbia, Hawaii, New Jersey, New York, Rhode Island, and Washington). The information, pictures, text or products presented on this website are not a representation by us, and should not be understood by you, that any product or completed firearm is legal to assemble or own in your state of residence. We encourage each and every builder to perform their own research about the state and federal laws that apply to them. It is your responsibility to understand the law and we encourage you to consult with an attorney or your local ATF representative.