I had problems out of a previously reliable upper.

Short stroking.  I disassembled the gun for cleaning and found the two screws on top of the bolt carrier were loose.  

Odd, they have never come loose before.  I thought it might be a result of using a silencer, with the added gas pressure.

I tightened the screws, staked the screws with the same dimples that had been used before.

I shot the rifle again, and within just a few rounds (maybe 15?) it was short stroking again.  Those damn screws were loose again.

I tried to stake the screws, but the material on top is kinda hard to 'dimple.'  

any advice?  Bigger hammer?  Gunsmith?

TRG

Locktite! The stronger of the red or blue.

Try new screws first, the old ones have probably stretched, or may have been small to begin with. The staking is mostly insurance against the screws (or the heads if they snap) getting into the action. Do stake them tho as it does add some restriction to them loosening.

LocTite burns, it's heat that loosens it. Just went through this on the range not too long ago, "But, but, I LocTited them!".  

For a "stake" tool I use any of the busted off 1/16" pin punches I have laying around ground down to a wedge shape. Helps to have a vise, lay the body of the carrier between the jaws and the key on top of one jaw. Be sure not to displace too much metal, the specs are in the TM. And if you get real frisky you can split the metal of the key over the head of the screw so go slow.

[some day I'll prufe then post, some day]

Damn.

I was hoping for something simpler.  New screws, punch pin, vice.  Oh well.  Guess I get to play gunsmith again.

TRG

Thank you for the detailed instructions.

When you loctite screws, you are locking the threads to the bolt carrier and increasing the chances of breaking off the head of a key screw.

When you stake screws, you are locking the head to the KEY.  This does not stress the threaded shaft when removing.

Also, the proper punch for staking is a [b]CENTER PUNCH[/B]!

BUY A CENTER PUNCH AND A 'PRICK' PUNCH.  A roll pin punch will not work worth piss for this.

Use the 'three point' technique shown in the military TM you can download

[url]http://www.ar15.com/content/books/TM9-1005-319-23.pdf[/url]

Use the prick punch to start your dimples and use the center punch to finish.

Remember, you are trying to push metal into the knurled outside of the head of the key screw.  You should start your dimple about 1/2mm outside the screw hole, not on the junction between the screw and the hole.

If you distort the edge of the key a little to where it will now rub on the reciever, stone it back down.

Good point aboutthe loctite.

FWIW, this problem did not occur until I began using a sileencer.  I suspect the added pressure and heat on the older bolt carrier is too blame.  I'll get some new screw and restake it.

TRG

I had this very same problem this weekend on a BM Superlight upper that I purchased NIB (with new bolt and carrier).  I had something like 750 rounds through it when it started to short stroke.

Nothing like your tricked out AR15 short stroking with a few muzzleloader shooters watching to make you feel all warm and tactical.  My shooting buddy kindly yelled (he was wearing muffs, I had ComTac's) "Maybe you're not holding the rifle solidly enough" and then proceeded to put his hand on my shoulder to held me manage the recoil.  Never mind us, gents, we're just playing with my poodle shooter.  [BD]

My assessment was that the initial staking job was not adequate.  I cleaned the bolts, reinstalled them and then put new stakes over the old ones using a small chisel and hammer.

There is definitely metal from the carrier key that was pushed over (and possibly into) the heads of the bolts.  It isn't the prettiest staking job, but it will certainly get the job done.  I made certain that a few small metal shaving that protruded up from the carrier key were filed smooth.

I don't think that I've ever had a firearm "come apart" in this manner before.  I don't want it to happen again so I made sure the stakes I put in were nice and solid.

No I didn't follow the TM.  I'm not a gunsmith.  And it's been a while since I've broken anything with excessive filing.  (Drop the dremel tool and step away from the 1911.)  But I am quite confident that this will hold.

YMMV

PS Any of the more experienced home gunsmiths please feel free to critique my methods.  I figured a carrier key and new bolts would be cheap to replace if I screwed it up.  I could've (should've?) just thrown in an extra carrier and sent this one back to BM for repair.  But I just couldn't resist....

My work seems to be in line with the -23.

Here's the relevant portions on page 131:



Perhaps the only thing that I could've done differently is use a punch of some sort.

Maybe I'll pull the bolt carrier tonight and compare it with my other ones.

FWIW, I staked on my Colt collapsable stock tube and, while it ain't pretty, it is very solid.

Here is my two cents worth. Loctite them with the green "retaining compound" Strongest,and stake them. I have been using Loctite for 25 years on my small block chevys,and harleys,and never had a nut or  bolt back off. Yes heat is used to defeat it but I don't think you will get your AR as hot as an engine that is run down the quater mile all day in the hot summer FL sun. And yes it works in oil,synthetic or otherwise,(rod bolts for one). So for you other's flame away if you like!

HeavyMetal,


Who said anything about using a roll pin punch?

IceMan_1,

Green (cylindrical locking) is more heat resistant than blue and red. Stakes are still needed to keep the heads of the screws in the carrier key if the screws snap.

Don't go looking for fights on here, Ed's place is open all night.

I'm not looking for a fight,and I didn't say anything about a roll pin punch! Edited -and I did say to stake them also!

Then don't tack "flame away" onto the end your posts. I did not say you mentioned roll pin punches. Reading is fundamental.

I stand corrected on my Loctite suggestion. I guess that is why I keep coming back here so much. Not everything that I have been told is accurate and I can learn something new.