What does "staked on" refer to ?

I was just reading thru the Bushmaster catalog (before ordering spare parts), and it says that the "bolt carrier key must be staked on". To what does this refer. My carrier key was a little loose recently, so I tightened it with the appropriate sized allen wrench. Is this good enough ?


CKMorley

According to the TM (downloadable from this site somewhere) the sidewalls of the carrier key are supposed to staked onto the allen screws. If they are not staked, they will come loose. If they loosen slowly, they will fatigue and break. If they loosen quickly, the rifle will start short stroking. Anyway, the TM shows how to do it.

to stake the gas key screws you need to take a center punch and swage material to physically keep the screw head from rotating under vibration/heating/cooling.

you'll see some screws staked in 2 places and others staked in 3 places per screw head.

more detail in the -23 manual:
TM9-1005-319-23&P - M16A2/M4 Maintenance (troubleshooting & repairing)
[url]http://www.mcdl.org/Manuals/Manuals/Maintenance/TM9-1005-319-23.pdf[/url]

Thank you for the info, guys.

CKMorley

most importantly, those screws are supposed to be torqued down. 35-40 in/lbs, then they are staked. Staking refers to the method of keeping a screw tight. Using a punch, put it on the top of the screw, pointing down and toward the carrier metal, then give it a whack. This should put a piece of the screw head into the carrier keeping it from turning. 3 times for each screw. Don't get excessive, just a nice little ding. A maximum of .025" protrusion of metal upward is permissable.

edited: Don't go straight down, go at an angle to push metal toward the carrier. Maybe 77 degress or so. Try it on something else first to get the feel!

courtesy of USMC Tech Manual TM 05538C-23&P/2

JET

Also check that the screws have deep enough knurling or notches to take the staking. I bought a new carrier/bolt assembly from Bushmaster at Camp Perry two years ago. After about 300 rounds, I was getting short stroking.A check of the bolt carrier showed that the gas key was loose. Although staked, both screws worked loose since the "notches" on the sides of the screw heads were nothing more than scratches. I cleaned and degreased the screws and holes. Then everything got Loctited together. 3,000 rounds later and it is still tight.