www.ModulusArms.com | AR-15 Jig Instructions
Milling the Rear Shelf Pocket
Note: If you bought a forged lower from Modulus Arms, you can skip to Drilling the Hammer, Trigger
and Safety Pin Holes. If you have a lower receiver that does not have a pre-machined rear pocket, you
must continue with this section.
Configure Jig for Milling Rear Shelf Pocket: Remove the screws attaching the front and rear support to
the template. Remove the screws attaching the template to the side plates. Remove the template.
Install the eight screws attaching the supports and side plates to 1 ft-lb as shown in Figure 23Figure 21.
Figure 23: Configuration for Rear Shelf Milling
Milling Fire Control Pocket: The end mill should already be installed in the router. Move the base of the
router until the tip of the end mill is at the first line in slot “B”, shown in Figure 24. Place the router into
the rear shelf template and into the opening from the previous milled fire control pocket. You will
always use this as a starting location for this step. Be sure not to be touching the sides of the opening
when you start the router. Start the router and allow it to come completely up to speed. Start to move
the router removing material. Start by moving in semi-circular motion in small clockwise steps. Press
down firmly to prevent the router from lifting. Do not try to move the router in one straight direction
but rather in smooth half circles removing small amounts of material as you proceed. Join the opening
with the two holes you drilled previously. When you reach the template, trace the inside diameter of the
template in a clockwise motion. Be sure to remove as much material as possible before touching the
template or tracing the template. Reducing the amount of time in contact with the template will
increase its longevity. Do not push hard against the template. A gentle touch is enough. Mill the
rounded corners in the template last, as they are most likely to chatter. When the opening is the same
size as the template turn off the router, wait for it to completely stop and remove it. Adjust the router
base so the end mill is at the next mark on the depth gauge. Continue in this pattern until you reach the
bottom of the depth gauge.
Note: DO NOT INSERT OR REMOVE THE END MILL FROM THE TEMPLATE WHILE THE END MILL IS
SPINNING. THIS IS DANGEROUS AND THE MOST COMMON CAUSE OF BROKEN END MILLS OR
DAMAGED JIGS/LOWERS.
Note: Be sure the end mill is very tight in the router. Tighten it as much as possible.
Note: If the router begins to whine or vibrate during milling, turn the router off and remove it
from the template. Inspect the end mill and be sure there are no chips jammed into the teeth of
the end mill. If there is, use a tool to remove the stuck chips. A small screwdriver or pencil works
well. Be sure not to damage the teeth.
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