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Sig P320 Series Part 1 Parts ID & Drill Guide (*update2)

Below is a complete tool list used for building the Sig P320 !

JSD Links lower parts



P320 Parts Kit

X-Carry Full Build Kit


Slide completion kit

Full list of Tools

Wen4214 Drill Press:

Drill Press Vice:

Drill Press & Vice Combo:

Tap Magic Cutting Oil:

Dremel Workstation:


Sig Sauer P320 Drill Guide

We have a total of 16 holes to drill (9 on the left & 7 on the right). There are 7 sizes of bits needed:

7 Different Bits

9mm (565) = 530 rpm

#22 (1274) = 1260 rpm

#9 (1020) = 940 rpm

#40 (2041) = 1730 rpm

#32 (1724) = 1700 rpm

#39 (2010) = 1700 rpm


We will use each bit once on the right side. On the left side, we will not use the 7/32. Also on the left side we will do (2) #22 holes and (3) #40 holes. You will see a hole on both sides marked P250. For this project on a P320 build we will not drill those holes.

Before we jump in and drill, lets knock out some general knowledge and best practices for this project.

A. Top Plate in When Drilling

- This provides appropriate backing to the FCU and prevents bending/flexing

- Reduces Drill Ring

B. Use Quality Bits

- You can use the bits that come with the Jig. They are not ideal for this project. The smaller bits #32, #39, and #40 in particular have a difficult time penetrating.

- I have some suggestions on the bottom of this post, however any cobalt bits should work well.

- We have a tool sharing program in the forum with 5 sets of bits for this project. They get checked out of the tool crib quickly, so follow the thread closely for availability.

C. Use Cutting Oil - 4 Common Errors leading to Smoke

- Not enough oil

- Speed is too fast

- Pulling down too hard on the Quill

- Leaving the bit in too long (sweep in making contact for a few seconds and out)

D. Work Efficiently

- As mentioned above, there are 16 total holes to drill. Completing all the holes on one side and then the other results in changing the bits over a dozen times. It will also require constant depth adjustments and realigning of the table. Reduce all that extra work by drilling all the holes for each bit. This method requires you to only have to flip the jig in the drill press vice and not reconfigure depth plunge every time.

Preparing to Drill

1. Secure the Bit into your Chuck. Here I am using a speed chuck to seat the 9mm bit. You may have a keyed chuck. One of the most common mistakes that occurs is users do not tighten all 3 posts on keyed chucks. Be sure if using a keyed chuck to tighten all 3 jaws.

Next we are going to adjust the drill plate height. With the jig in the drill press vice you should have no more than a 1/2 inch of space between the head of the bit to the contact surface of the Jig. Remember we have the largest bit in (9mm) and as we step down to smaller and smaller bits that space will increase organically. Starting out with too much space will lead to longer pulls of the quill to close the gap. The less we have to turn that quill the better.

Now I'm going to remove the drill press vice and jig from the plate. We must have a drill plate that is level and true. It is essential to the outcome of the build that the holes are exact.

Using a level and the drill plate adjustment knobs we will insure our work surface is true. Here I am using a digital level that reduces any room for error.

Digital Level

Standard Bubble Level

With the bit secured and the table level, we now want to verify the bit is straight and true. Using a machinists square, mini carpenters square, or a right angle tool ensure the bit runs straight down with no gaps.

Put the drill press vice with Jig in it on the drill plate and align the 9mm hole. I always prefer to have the piece I'm working on centered within the drill press vice. To accomplish this use high strength machinists magnets as spacers. This particular drill press is a wen4214 and has a laser alignment feature. Once we are aligned secure the drill press vice to the drill plate using clamps or bolts.

Our last step before drilling is to set our depth stop gauge. Here we will calculate the plunge depth and adjust the depth stopper. There are 2 key measurements we need in order to set the proper drill depth:

  1. Flute Depth

  2. FCU Jig Depth (see jig depth measurement below for each hole)

Calculate the flute depth by measuring from the tip of the bit to the middle of the first flute. Every bit is different, but in this particular example the flute depth for this bit is 1/2 inch.


Rotate the Quill down until you make contact with the FCU. This is your contact Depth. From this point, move the stopper knob to the sum of the Contact Depth + Flute Depth and tighten. Each bit is a different size and will have a different flute depth. Ensure with each change of bits that you are recalculating the proper depth stop.

Set the correct speed for the bit (refer to above diagram) This is the 9mm and the wen4214 has a digital adjustment that I will set to 565rpm. One last check - you've heard the old saying measure twice cut once - well MGB has a saying for Gunsmithing "Check 3 times and you're fine". So one last check with the machinist square from the bit to the drill piece and we are good to go

Apply tap magic oil to the hole and onto the bit. Turn on the press. Using the quill pull down making contact with the FCU. Develop a rhythm of touch and go. Sweeping in for a few seconds and releasing. Every few sweeps, clean off the debris with a cleaning brush and reapply oil to the hole.

If smoke appears stop and assess 3 common problems – (A) Downward pressure to much or too long (B) Speed is too high (C) Need oil

Have a build question or just want to hang out to learn or share the best build techniques ? Join uss at the MGB Forum!!!

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