So, take a cue from experience. Adjust the catch button so's it's just about flush with the inner groove or just sticks out a tiny bit. This'll make the catch firm enough to prevent accidentally bumping the button and letting the magazine drop out-yet it won't be so tight that you can't pull the mag out for a quick re-load.

Here's why: If you jam the receivers closed while the selector's in the AUTO position, you'll force the automatic sear down and damage the automatic sear, and the sear pin, and will likely rough up the bottom of the bolt carrier.

That's 'cause when the selector lever's in the AUTO position, the tang of the automatic sear moves to the rear. You can see how it works by opening the receiver and turning the selector to AUTO and watching the movement of the tang of the automatic sear.

So-o-o... do it right... every time. Point the arrow to SAFE. Then the receivers will close without any interference.

Make a habit of checking the FIRING PIN RETAINING PIN regularly. Some guys've been losing theirs...which could embarrass the life out of you. A loose firing pin retaining pin with one or both tangs broken off won't cause a malfunction. But, be careful that the retaining pin doesn't drop out and get lost when you're removing the bolt carrier. And after cleaning, be sure you replace the firing pin. Then secure it with the retaining pin. Check it again when you're assembling the bolt carrier to the receiver.

5