The day your frame arrives: what to check before you cut

Ten minutes of checking before the first drill bit touches the frame saves the week where you discover a missing part halfway through.

Count the kit

Frame, front locking block rail, rear rail module, jig halves, pins for the jig, 3 mm drill bit, 9 mm drill bit, 9 mm end mill. Photograph the contents as you unpack; it settles any question later.

Inspect the frame

Look down the magwell for moulding flash, check the rail tab areas are intact and unchipped, and confirm the accessory rail is square. Polymer shrinks slightly as it cools, so light sink marks on thick sections are normal and cosmetic.

Dry fit the jig

The frame should sit in the jig without force and the jig should close without gaps. If it rocks, find out why now rather than after a hole is drilled.

Check the rails against the frame

Set each rail module in its seat before any cutting. It will sit proud; that is what the cuts are for. What you are checking is that it seats square.

Confirm your other parts arrived

Slide, barrel, parts kit, magazines. Confirm the parts kit contains a locking block and the three pins, because that is the most common gap.

Then set up

Vise, drill, file, safety glasses, cutting oil and good light. Work when you are not rushed. The frame is the one part of the build you cannot undo.

This is general information, not legal advice. Laws on unfinished frames and receivers vary by state and city and change often. Check the current law where you live before ordering.