80% Sig Sauer - P320 Compact Double 9mm Luger 3.9" 10+1 - 2 Mags - Black Grip Black Nitron Stainless Steel
Glock Magazine - OEM 19 9mm 10rd PKG

80% Sig Sauer Jig - P320 Compatible - MUP 1


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Modular Universal Pistol 1 Completion Jig

Operations Required to Finish:

  • All Holes
  • Bend Slide Rails
  • Trim Rails to Size

Jig Kit Includes

  • Jig
  • Top Plate
  • Drill Bits

2 Side Plates 1 Top Plate 7 Drill Bits 4 Bolts

Recommended Tools

  • Dremel
  • Vise
  • Drill Press
  • Files

MUP-1 Jig Instruction

1. Assembling the jig

1.1. Place the two side plates together and secure them with the provided bolts. Do not tighten all the way.

  1. 1.2. Place the 80% MUP-1 Receiver into the jig. Ensure the receiver bottoms out in the jig.
  2. 1.3. Tighten the bolts.

2. Bending the slide Rails (approximate .860” from outside of rails)

  1. 2.1. Secure the jig in a vise with the rail tabs sticking up towards the ceiling.
  2. 2.2. With the receiver bottomed out in the jig, and the bolts tightened, place the contoured end of the top plate in between the first set of rails. Be sure that the ‘top’ of the top plate is now facing the ejector pin in the 80% MUP-1 receiver, so that you don’t bend it as you start the rail bends.
  1. 2.3. Using a hammer, pound the top plate down to start the bending process of the slide rails.
  2. 2.4. Repeat step 2.3 for the second set of rails. PLEASE NOTE! This first step only starts the bend for each set of rails.

2.5. Loosen the bolts slightly, and with the receiver still in the jig, place the top plate down in to the receiver. Be careful to assure the top plate is aligned such that the ejector is not being contacted by the top plate.

  1. 2.6. Tighten the bolts and place the jig on its side into a vise.
  2. 2.7. Squeeze the vise closed until the top plate fully bends the rails on to the side plates and bottoms out. Both front and rear rails need to bend to the side plates. If need be, use a punch to finish the bend of all 4 rails flat to the side plates.
  1. 2.8. Remove the jig from the vise and rotate it so the rails are facing up again.
  2. 2.9. Using the line marked on top of the side plates as a cutting guide, remove the excess material on the slide rails using a Dremel.

3. Drilling Holes
3.1. Keeping the top plate and receiver in the jig, place the fixture on its side and squeeze it in a vise so that the top plate is bottomed out and rails are again tight to the side plates
3.2. Drill all the corresponding holes. We recommend using a drill press, but a handheld drill may work as well.
3.3. Drill one side, then the other side. DO NOT DRILL FROM ONE SIDE THE WHOLE WAY THROUGH TO THE OTHER SIDE.

NOTE! The two closely-spaced #40 holes are intended to be a slot. Cut out the material between the two holes.

4. Trigger and Safety Slot

4.1. While the receiver is in the jig (Opening where you used the 7/32” bit), use a Dremel with a cut off wheel to open the trigger slot. This opening needs to have enough material removed to allow the trigger to pass through that opening.

4.2. On the opposite side of the trigger slot, you drilled 2 small holes (#40). Using a Dremel or a file, remove the material between those holes to make 1 opening.

5. Final Steps

  1. 5.1. De-burr all holes.
  2. 5.2. Contour (if necessary) and de-burr the slide rails. On occasion, the Dremel method does not remove enough material to allow the MUP-1 to fit inside the slide. If this happens, remove material using a metal file or Dremel little by little on both left and right sides to ensure a proper fit. If you are using a Dremel, use it at the lowest speed and go slowly – you can always take more material off, but you can’t easily add more on.

6. Assembly

6.1. Using the parts you’ve acquired, assemble your completed MUP-1 receiver. There are several videos online; at the time of this document’s writing, check out our video at the top it will take you through the whole process:

“SIG Sauer P320 FCU/Lower Reassembly”
6.2. Using your Cal-X kit (or other grip and slide assembly), function-check your firearm to assure

that the trigger function works, and resets as desired. 6.3. Take your new firearm to the range and enjoy!



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