Colfax Tactical

308 jig

The 308 jig was designed for the builder with moderate experience. Although it can be done, it

was not designed for a drill press. It was designed specifically for the Colfax Tactical 80%’er.

There is a right and left half to the jig. The image above is viewed from the left side. The buffer

will sit to the right as shown in the above image. There is a long dowel pin and two short dowel

pins. The longer pin will be used in the pivot pin holes and the shorter two pins will be used in

the take down holes.

The left half includes the hammer, trigger, and selector guide holes. They are 5/32, 5/32, and

3/8 respectively.

The image to the left shows the two halves

with the standoffs in place, two 10-32

socket head cap screws, the long dowel,

and the two shorter dowel pins.

The image to the right show the jig viewed from the

right side. We recommend the use of low adhesive

painter tape on the side of the lower to protect

the anodized surface from the standoffs.

These two images show the

tighening of the 10-23 cap screw

while adjusting the ¼-20 push

screw. The goal is to square

sides of the jig.

Measure as you adjust to

insure parallel sides.

The next step is to scribe the center line of your forging. This is necessary because due to the

nature of forgings, they will vary from one to another. A simple method is as follows: Measure

the upper rim width of the fire control body area. Divide that number by two. Set your calipers

to that number. Scribe the line as shown below.

Line up the right edge of the top

plate with the scribed lines on top

of the jig sides.

Line up the top plate scribed line with your

scribed forging line. You will see that the top plate

holes are slotted. This is because no two forgings are

exactly the same width. As such, slight adjustments

are necessary to center it.

You are ready to machine!

Below are some basic measurements.

The coordinate origins are as follows:

X = 0 in the center of the pivot pin (the diameter is 0.2770”)

Y = 0 in the center of your specific forging.

You can pre drill the five 7/16” holes and the ½” hole for easier milling. The coordinates

are shown.

4.0481 in

5.6921 in

6.2193 in

7.1130 in

7/16 drill

1/2 drill0.1270 in

0.1270 in

The remainder of the coordinates are self explanatory and may help the builder with

moderate machining skills.

3.8301 in6.4380 in

4.6481 in5.0161 in

R0.1560 inR0.1560 in

7.3630 in

R0.2500 inR0.2188 in

4.1679 in

5.0109 in

6.1359 in

0.3485 in

0.6625 in

0.4375 in

1.2495 in0.6300 in