Proper Staking of carrier key screws.
Last Updated :: 1/3/2006 11:51:39 PM


This is the second carrier I've worked on from the same vendor in two days
and the second one that the keys have come loose in less than 100 rounds.

Staking like this DOES NOT SECURE the head of the screw it only manages to
damage the head of the screw enough to keep a wrench from fitting it.

There is a reason the screw heads are striated along their exterior,
stake the key INTO the striations.

You can see the misalined stake marks on top of the key and screw heads here





the screws (like the previous one) were not even finger tight when I checked them.

Stake your carriers this way




this is the easiest method of which I know



if you work on ARs and don't have a vise you are a NOGO, buy one of the cheap Chinese $19 ones from Harbor Freight or whoever is local to you.

There is no excuse, it is a manadatory tool for even a would be AR wrench. Get on it.

Stake tool is homemade, ground on a belt sander from the stub end of a busted 1/16" pin punch.




There is no excuse for shoddy workmanship, people's lives are at risk with every sloppy build.


Originally Posted By Tweak:

Originally Posted By GhostRing:
Are you hitting straight down or at a 45* angle?



in the side staking photo? don't worry about number degrees or angles just displace key metal into the heads of the key screws. even if you hit the key at a perfect oblique it'll only push where there is the least resistance so the stakes often come out angled.

at least having to pull the keys gives me a chance to lap the key to the carrier, both were pretty rough.




Originally Posted By m24shooter:
Staking is forcing some of the metal onto/into the surface of the key/bolt/nut whatever to prevent it from backing out. In the case of the gas key, if that puppy comes undone while in operation you will have a rapid deconstruction of your rifle. It will probably be a significant event in your life.
The receiver end plate/sling plate on the back of CAR/M4s is staked into the castle nut to prevent it from walking out.
ETA because I assumed you had a basis of knowledge, which you indicated you didn't: to stake something you place a staking tool (Tweaky uses a ground down punch as shown) onto the upper side of the carrier key (in the above example) adjacent to the key screws and whack it smartly with a hammer. this forces some of the metal from the carrier into direct contact with the striations on the outside of the key screw, preventing it from backing out. Sorry to leave that out.




Originally Posted By TonyRumore:
Actually, rather then hammering on the thing at all, I prefer to use a specially modified set of bolt cutters. The jaws are cut back so when the handles are closed, it squeezes the key just the right amount, equally on both sides. If you look at a Colt bolt carrier, it appears they are using a similar type of tool.

Tony Rumore
Tromix Corp




Originally Posted By Stickman:
Tweak, your pictures make my eyes bleed, but its a good reminder that people should be checking their staking when they pick up a new/ used AR15.

Here is a picture of a properly staked carrier that I just picked up. Three guesses what company.....




PS- I confess I like the picture of staking in the vise, that is going to save some aggravation for first time stakers!!




Originally Posted By boltcatch:
Top to bottom, BCG pulled from a new Sabre upper, CMT M16 BCG, and RRA enhanced carrier.



If that one in the middle comes loose, I'm going to be pissed.




Originally Posted By QUIB:
Top is my Oly carrier with factory stake job. Below is my carrier from Del-Ton which I believe is from CMT. It was not staked from the mfgr and I double checked the torque before staking it my self. My homemade staking tool is also pictured.





Originally Posted By KA3B:
Oly


Fulton


Oly


Bushmaster




Originally Posted By Taffy223:
We used to use "staking" locking quite a bit where I used to work (100 times quicker than wirelocking). All the components I worked on were military aircraft parts ..either hydraulic pneumatic or mechanical. Our Staking tool that would be used in very similar circumstance to the AR15 screws mentioned here was "round". It was more like a centre-punch and was placed alongside the head but on the outer edge and given a good clout forcing the matierial into the head.

It worked very well and I cannot remember us having problems with locking even in the most demanding opperating environment.




Originally Posted By Taffy223:

Originally Posted By boltcatch:
Top to bottom, BCG pulled from a new Sabre upper, CMT M16 BCG, and RRA enhanced carrier.

i2.photobucket.com/albums/y41/boltcatch/carriers.jpg

If that one in the middle comes loose, I'm going to be pissed.



IMHO the top one has the firmest locking...the middle one would not be adequate for aircraft work.
It's squashed down ...not into/across




Originally Posted By Tweak:

Originally Posted By blueheeler66:
Tell us more on this lapping.



Put a couple drops of oil on top of the carrier and slide the key across it's mating surface until it stops dragging. Usually the mouths of the screw holes have burrs on them as well as being raised slightly above horizontal. There are often matching burrs on the underside of the key. Better gas seal and a cleaner mating surface so the key won't come loose once the screws are tightened and shot.

Once your key is staked go out and shoot a couple dozen rounds through the rifle and RECHECK that your screws are tight.




Originally Posted By JasonC:
The manual says to stake it in 3 places...





Originally Posted By Tweak:
this is the pic most folks come up with



That is field replacement staking, good enough to get a rifle back on the line but not factory correct.

How to stake carrier key bolts




Originally Posted By HeavyMetal:
I staked a CMT carrier for a friend that was exactly like in the first picture in this thread.

I had to hammer the hex wrench into the bolt head because they had deformed it. From the alignment marks after tightening the bolts to where they were originally when staking was factory attempted, they were about finger tight as Tweak stated.

CMT makes excellent product for the money but they really need to invest in proper tooling/training for carrier key staking.

My advice for vendors would be to check these and fix them in house before they ship them out, it will cut back on the future RMA's and will probably net them less work. Also for them to lean on CMT to fix it at the source.




Originally Posted By dennysguns:
I have a product called "Rockset". It is a 1200 degree cement. I use it to secure suppressor mounts like Gemtech Bi-Locks, Troy's, Surefires etc. It is the same material that Gemtech used to supply with their cans. I got the 411 on the product from Phil Dater.

This might add some extra insurance on carrier key screws. Stuff is relatively cheap at $15 for 2oz.

I have done a lot of suppressor mounts over the last 2 years and still have over half of the original bottle left.

Denny

Oh yeah, good luck getting it loose




Originally Posted By JosephR:
damn it! I just checked my Bolt Carrier that came from ADCO in my DMM4 midlength upper. It is supposedly a WOA Carrier and Bolt.

In this picture it looks like the top marks don't even contact the screws. The bottom marks DO appear to contact the screws, but I can't say they really do. It's more like the screws and carrier key just both got nailed pretty hard and both lost a little material.


Here you can clearly see how the staking of the 'bottom' marks actually damaged or appear to have damaged the grooves along teh top edge of the key.


This looks like absolute shit. I don't remember them looking like this. Maybe I'm thinking of an old carrier I had. I'm debating whether or not to crank down on these to see if I can get them loose AND I'm tempted to filed that displaced material away from that 90d groove...




Originally Posted By PBIR:
So the consensus is that the CMT process is incorrect and therefore unsafe?





Originally Posted By Tweak:

Originally Posted By PBIR:
So the concensus is that the CMT process is incorrect and therefore unsafe?



not unsafe, just prone to loosening and incorrect.




Originally Posted By Tweak:

Originally Posted By JasonC:
Yup. FWIW, the manual states the hex screws should be tightened to
35 to 40 Inch-pounds (3 95 to 4 52 N m). (I have been reading the manual lately- anticipating my middy build)



That number is hideously low, no doubt to keep thick headed armorers from shearing off screw heads. Take them down tight then a smidge more.




Originally Posted By sodacan_slayer:

Originally Posted By Tweak:
Oddly it's the Armalite tech letters that mention "the book" numbers being too low and that they learned this after dealing with a lot of keys. Guess I should start looking for an in/lbs wrench of my own just to get a read on my torque value.



I'm guessing this is the tech letter you are talking about. It says torque them down to 55-60 in./lb. Here is a link to the tech letter for anyone who wants to read it. There sure is a lot of interesting stuff in those tech notes

Armalite Tech Note on carrier key screws

Also, oddly enough, the armalite tech note listed in order just before the one above covers the "Heating the barrel to 1200 degree's" issue. Here is a link to it.

Armalite Tech Note on barrel heat - Notice the section titled "Effect of heat on the barrel"




Originally Posted By Tweak:

Originally Posted By Mdripley:
Just checked out my new BM boltcarrier and it looks like the staking failed to displace metal into the key screws. I guess I will restake them to be safe.



you're best off to pull the key, lap the key into the carrier, then reinstall the screws making sure they're tight, then restaking. At the very least make sure the screws are tight before restaking.




Originally Posted By geerhed:

Originally Posted By geerhed:
My new BCG...manufacturer unknown at this time (will edit).




Per mongo's opinion here, it is probably DPMS.

Thanks to this thread, I checked the screws and they were easily loosened. I was going to test-fire this on Monday. Thanks guys.




Originally Posted By bionicmonkey:
yikes.. thanks tweak for posting about this.. I opened up all 3 uppers and ouch - found this.

Top is Bushmaster (both my BM's look very similar), bottom is brand new CMMG upper I got this month (cmmg refuses to name their supplier).



close-up of the stake seems to show that it was punched vertically rather than slashed horizontally.


I dont own a vice, should I A: field punch it, B: lay it on its side and side punch it with a screwdriver, or C: go and buy a vice?

thanks..




Originally Posted By AtlantaFireman:
Tweak,

This is good information on a very important topic!

I have a bolt carrier, maybe two, that have the staking going across the bolt heads, like your photo shows. Looks like that I'll need to do the job right, just in case....I like my face and eyes the way they are now: INTACT.

When I used to build rockets and stuff, we would stake our bolt heads like you show, not across the bolt head itself. A few engineers helped us build a rocket engine once, they did not stake all thier work. During a test firing, bolt came out, and engine was toast....actually more burned to hell and back rather than toated. After that we left "Poindexter" ("Dex" to his friends) do the design and WATCH us build it. Of course, he was the same one who tossed a lit road flare in a styrofoam ice chest, which was half full of liquid oxygen....Wiley Coyote!!! hahahaha But that's another story.




Originally Posted By Tweak:
if the screws come loose the worst that happens is your rifle stops working. worst case scenario is the caps snap off of the shanks and get into the upper causing the carrier to bind. nothing life or limb threatening.




Originally Posted By DrMark:

Originally Posted By Tweak:

Originally Posted By ChuckT:
Does anyone know what size hex wrench is needed for the carrier keys?



Two sizes are common, one is listed above and I'm too lazy to go look up the other one right now



I just checked the wrench size needed for the 2 dirty guns that are on the floor a few feet from me...

LMT BCG - 1/8 in.
CMT BCG - 9/64 in.

Speaking of lazy, I guess I should be cleaning the guns instead of playing with hex bits and posting...





Originally Posted By Triple_D:

Originally Posted By Tweak:
AAMOF, if my eyes aren't mistaken I think I see both sizes of screws in that pic, can you confirm boltcatch?



LOL!

So you want to see different types of bolts huh? Check this out.




I guess my eyes aren't what they use to be, because I didn't even notice the difference until I took the picture and blew it up.