On loose carrier key screws

[Duffy]

That Young is so adamant about not needing them and apparently recalcitrant and combative, so much so as to publish a paper on their site with what I deem is false and merely his opinion is enough I'd not buy their BCGs.

Will had strong opinions about this as well, his came from having seen numerous gas keys screws fail first hand. I trust Will's experience and opinion.

[lysander]

It all depends on how you see them fail.

- Screw head breaks just under the head. These are usually the result of over aggressive staking that winds up side loading the screw head (FM 1). This is why the diameter of the head needs to be controlled very tightly so there is little play between the head in the counter bore. The other possibility is the screw was over-torqued during assembly (FM 2). If you look at the fracture surface, you can tell which failure happened, An over-torque will result in the 45 degree shear plane, side loading in a 90 degree plane.

- Screw is loose. This can have several causes: (FM 3) Insufficient torque to start with. (FM 4) Dirty mating surfaces during assembly giving a false clamping at specified torque. (FM 5) Over-torque, but instead of cracking the screw, the threads yields. (FM 6) threads yield under service loads (in this application, highly unlikely as the forces in the axial direction are rather modest). (FM 7) Screw un-screws itself under service conditions. (FM 7) Tampering, or unauthorized removal of the screws.

In the AR design, only the last the last two failure modes are mitigated by staking, so the argument to not stake does have merit. The primary reason the Army wanted staked screws was to prevent Private Snuffy from thinking it was okay to remove and clean under the carrier key (or, maybe Sergeant White-Gloves, and Lieutenant Inspection).

From what I have seen in broken screw heads: side loading is the biggest problem.

The biggest advantage I see with Ned's OCKS knurling, is that it gives excessive material displacement most people seem to feel is necessary a place to go before it starts to bear in the head of the screw and side-load it. (And, keeping the head dimension consistent, that itself is worth a good bit.)

If you read the drawing requirements, staking is only supposed to add 5 - 45 in-lbs to the removal torque. That does not require much in the way of material displacement.

Oh, and if you use a MOACKS, or similar tool - Tighten opposing screws at the same time, do not tighten down one side, then tighten down the other.

[Dutch110]

Does anyone know when Young stopped staking? I have one of their N/M carriers that is well over 10 years old and the staking on it is near perfection. I could have swore I bought it direct from them back then.

[Dutch110]

Ok maybe "near perfection" was a stretch but not bad

[georgeib]

Ok maybe "near perfection" was a stretch but not bad

Weird that after all that they would use Chinese bolts. Wow.

[Dutch110]

Weird that after all that they would use Chinese bolts. Wow.

You know I never noticed that until I took that picture. Time to replace the key and screws or just retire it in general.

[Dutch110]

I was thinking about this thread the other day and laughing to myself. The guy (me) running the "no one considers the true cost of quality" flag up the pole is the one who has chinesium gas key screws on his high dollar BCG. Oh the irony........

[georgeib]

I was thinking about this thread the other day and laughing to myself. The guy (me) running the "no one considers the true cost of quality" flag up the pole is the one who has chinesium gas key screws on his high dollar BCG. Oh the irony........

I know you're not alone. Just buy some of Ned's screws and call it a day. They're available at BRT and FCD.

[Disciple]

Weird that after all that they would use Chinese bolts. Wow.

Please don't conflate Taiwan with China, or abandon them to it.

[georgeib]

Please don't conflate Taiwan with China, or abandon them to it.

Yes, the screws are actually made in Taiwan, ROC (which stands for Republic of China) in contrast to the People's Republic of China. Still Chinese, and most importantly, still notoriously low quality compared to mil-spec screws.