Function checking a finished Polymer80 pistol before the first range trip

A finished 80% frame is the start of the job, not the end of it. Before a completed pistol goes to the range it needs the same function check an armourer runs on any repaired handgun. Every step below is done with the pistol unloaded, the magazine out and the chamber visually and physically checked twice, in a room with no ammunition in it.

1. Clear it, then clear it again

Drop the magazine. Lock the slide back. Look into the chamber, then put a finger in it. Ammunition in the room during a function check is how people get hurt, so take it somewhere else before you start.

2. Slide and barrel fit

Hand cycle the slide twenty times. It should run the full length without binding at the rails and return fully into battery under spring pressure alone. Binding near the back of the stroke usually means a rail tab was left proud during finishing; file the frame, never the slide.

3. Trigger, reset and wall

With the slide in battery, press the trigger. The striker should release cleanly. Hold the trigger back, cycle the slide, then release the trigger slowly until you feel and hear the reset. Do this twenty times. An inconsistent reset is the single most common defect on a first build and it is almost always the connector or a dragging trigger bar.

4. The drop safety

Look at the striker safety plunger through the ejection port. It must lift clear only when the trigger is pressed, and it must drop back when the trigger is released. If the plunger does not move freely, stop; the pistol is not safe to fire.

5. The out-of-battery check

Push the slide back about a quarter inch and press the trigger. The striker must not release. A pistol that fires slightly out of battery is dangerous and means the trigger bar or the rear rail module is not sitting where it should.

6. Magazine fit and release

Seat an empty magazine and tug it down. It should lock. Press the catch and it should drop free under its own weight. A magazine that falls out on its own, or that needs a shake to release, points at the catch from the lower parts kit rather than the frame.

7. Slide stop

With an empty magazine seated, hand cycle. The slide should lock back on empty. If it does not, check the slide stop spring leg is sitting on top of the locking block rail and not trapped under it.

If anything fails

Stop and fix the one thing before moving on. Do not take a pistol that failed any step above to the range to see whether it settles in. It will not. Most failures trace back to three places: a rail tab left proud, a fire control pocket finished short of the jig line, or a small part reused from a worn donor gun.

First live fire

When every check passes, start with a few single rounds loaded one at a time rather than a full magazine, and check that the brass is ejecting consistently to the same place before you load it up.

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.