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0087-23 Quick Tip - Witness Marking Screws_Thumb

Quick Tip: Benefits of Witness Marking Screws

Author Caleb Savant
11 months ago
You've built your dream rifle, perfectly fitted and tuned exactly the way you want it. What happens if it has a screw loose? No, we're not talking about your AR-15's mental health, but how will you know if a screw backs out and that perfectly fit-together rifle starts getting out of alignment? Brownells Gun Tech™ Caleb Savant has a simple answer: grab a Sharpie or a paint pen and mark the screws. Draw a line on the head of the screw and carry the line to the area next to the screw. A quick visual check of this "witness mark" will tell you instantly if that screw has moved.
You arrive at a match after a bumpy drive, pull the rifle out of its case, and you can immediately see if all the screws are still, as the British say, "tickety-boo"! Or maybe you take a fall, drop the rifle, or smack it on a barrier during that fast-moving 3-Gun match - instant check again. If your shots are all over the target, and you suspect your optic's mount has come loose, a quick check will tell you that nope, you're just not shooting very well today.
You can witness mark any screw, such as handguard clamping screws. But this trick is probably most useful on anything that'll cause you to shoot worse it if goes out of zero - optics and optic mounts. The one catch is you probably only want to witness mark screws on guns where aesthetics and the condition of the finish are not important.