Staked carrier bolts, Shrouded pins... AR questions


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wacki
November 5, 2008, 10:02 PM
I found this complete buyers guide for ARs:

http://forums.officer.com/forums/showthread.php?t=81462&highlight=jwise

How important is it to have a shrouded pin? I have a carrier group that is fully shrouded but I can jiggle the pin so it falls outside of the shroud by about 1/3 a centimeter.

Also, they make a big deal about having solidly staked carrier bolts. What kind of symptoms can you expect when those screws come loose? Has anyone here actually had them come loose on you?

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mr.scott
November 5, 2008, 10:35 PM
The only time I have ever heard of a bolt failing by the screws backing out is at a training course where someone was putting thousands of rounds through the gun in short order. If you are a once a month casual shooter, I doubt you will ever have a problem.
If it concerns you, you can stake it yourself.

nicholst55
November 6, 2008, 03:03 AM
I hear lots of anecdotal stories about carrier keys coming loose; some brands are worse than others - Bushmaster had a terrible reputation for this for a long time.

What failures will it cause? Look up 'short recoil' in the troubleshooting section of any manual.

Gary G23
November 6, 2008, 08:42 AM
I had a Bushmaster once that short stroked when the screws came loose.

taliv
November 6, 2008, 08:46 AM
take that guy's recommendations with a big handful of salt.

Onmilo
November 6, 2008, 09:04 AM
A staked carrier key is pretty important and mil-spec requires it.
This is a carrier using mil-spec screws which have serrations on the sides of the screw head to better facilitate a secure bearing surface for the staking.

I have posted this picture before and have had folks comment that the staking is too light.
Shhhhh, I am going to let you in on a little secret, this is a mil spec carrier.
http://www.fototime.com/C9F3E39F401E57E/standard.jpg

A shrouded firing pin is importand if yhou are using most versions of the twso stage trigger.
The redesigned hammers used with these trigger assemblies can become caught in the opened pin tunnel causing a very interesting stoppage.

The opened up firing pin tunnel was a Colt design that when used in conjunction with a Colt modified semi auto hammer would lock the rifle up if somebody got the bright idea that all it takes to make an AR15 full auto is to remove the disconnector.
It serves no other useful purpose and is really not neccessary in any semi auto gun.
Remove the disconnector and the gun usually fires, at most, five rounds before something breaks, usually the firing pin.
A shrouded carrier is shown on top and an open tunnel carrier is shown on the bottom of the picture
http://www.fototime.com/852241DA3906015/standard.jpg

UniversalFrost
September 15, 2010, 12:32 PM
yes, the mil-spec as issued weapons I have carried are often "not acceptable" to the many mall ninja's that say you gotta have this and that and your staking needs to be as deep as the grand canyon.. serious

also another little hint is that some blue loctite works wonders on the screws (and the free float tube threads, and the the castle nut).

i do prefer a fully shrouded carrier though for my "toys" but one of my recent builds does have an old bushmaster carrier that is partially shrouded and I have over 7k of 5.56 thru it and have had no problems other than a little bit of marring of the hammer initially on each lower it is mated with.

briansmithwins
September 15, 2010, 01:06 PM
I've seen quite a few broken FPRPs on the unshrouded bolt carriers. I would not use them for that reason alone.

Staking is the origianl method for securing the gas carrier key bolts. It works and is uneffected by heat pr solvents, unlike Loktite. BSW

Bartholomew Roberts
September 15, 2010, 03:06 PM
Onmilo gave good advice.

How important is it to have a shrouded pin? I have a carrier group that is fully shrouded but I can jiggle the pin so it falls outside of the shroud by about 1/3 a centimeter.

The main issue is you don't want the firing pin collar to stick out. If it does stick out, then the notched hammers will occasionally grab it and slam it in to the firing pin retaining pin, bending/breaking that part over time. That is the most common issue I see with the unshrouded carriers - but it can cause the type of stoppages that Onmilo described with certain hammer combos.

What kind of symptoms can you expect when those screws come loose? Has anyone here actually had them come loose on you?

When the screws come loose, the seal between the carrier key and the carrier is broken and gas flows out the gap instead of into the bolt carrier - as a result, the rifle will short stroke or become a single-shot depending on how big the gap is.

Vibration can loosen machine screws that aren't staked or otherwise secured. Vibration can come from heavy shooting or even just riding around in the trunk of your car. I've had all kinds of parts come loose: grip screws, rail handguard retaining nut, castle nut, rear sight locknuts, etc. I've also seen several rifles with shortstroking issues due to improperly fastened carrier keys.

For me, staking is a big deal because it is really easy to do and it directly addresses a common source of problems with AR15 function. If a manufacturer doesn't have the time to properly stake a gas key, then there are probably a hundred other areas they might have cut corners on that aren't as obvious. It isn't difficult to fix; but it is something I shouldn't have had to do.

If you enjoyed reading about "Staked carrier bolts, Shrouded pins... AR questions" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!