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Posted: 2/25/2010 9:04:21 PM EDT
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I recently purchased a BCG from BCM. Everything looks nice but I am a little concerned about the adequacy of the staking. This is my first build, my fiirst AR, so I would really appreciate any input that could help me safely construct and operate this machine.
http://i890.photobucket.com/albums/ac107/gennovations/Staking.jpg |
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If that BCG was from any other manufacturer than BCM you would have 100 drinker's of the cool-aid chime in and say it is shit. Hell, you might even get some to dispute if it is BCM cause ..........never mind. I don't drink cool-aid and I say run it. It will shoot paper and pop cans just fine. Welcome to the site and happy shootin.
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The key in the picture is adequately staked. Some people like "aggressively" staked screws, screws that take a breaker bar to remove if and when... The real problem isn't "better than adequate," it's "nonexistent" staking. As noted, the metal of the key is firmly staked into the knurling of the screws-both of them-which means those screws aren't going anywhere. More here isn't necessarily better. Less could be a problem though-and in my opinion, Loctite is not a substitute for decent staking.
If I wanted to NEVER have those screws move a micron, I'd get 'em tack welded. I would prefer to have the screws retained instead of permanently fixed, so I would go with the BCM staking just fine. But I wouldn't want much less than what's pictured. |
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I would say they're not by any means optimally staked. There is no "dig" whatsoever into the hex nuts.
BTW, anyone who tells you that staking isn't important is FOS. Gas keys coming off of the BCG are one of the most commonly seen causes of major malfunctions, especially on weapons that have a lot of rounds through them. |
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I'll take it off your hands for $40. 
no way dude. But seriously, my goal is to make the most rugged and reliable rifle I possibly can. I want it to do whatever I want it to do. Function is definitly going to win over form on this rifle. So, I may look into staking it some more. I was expecting to see a little more dig into the screw-heads, but I had no idea about the knurling on their edges. I also don't want to get into a situation where I am unable to stake another key on it in the future if I may need to. Overall I'm pleased with BCM's products and specs; I just recieved their 20" upper today. I considered constructing an upper myself but since the front sight base requires tools I don't have to accurately index and attach to a fresh barrel, I decided to let these guys turn the wrenches if I can't do the entire thing by myself. looks good. big. |
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I agree-not "optimally" staked is a good description. But there IS sufficient metal pushed into the knurling of the screws that it would take quite a lot of effort to dislodge them. Slightly more aggressive staking, so that some of the screw head material was displaced, would be much closer to optimal. But not much more than that; some of the "I did it myself" staking pictures I've seen here looked like the person really seriously weakened the key around the screw heads, which wouldn't let it get loose, but would rather allow the key to break at the screw holes...
I would say they're not by any means optimally staked. There is no "dig" whatsoever into the hex nuts. BTW, anyone who tells you that staking isn't important is FOS. Gas keys coming off of the BCG are one of the most commonly seen causes of major malfunctions, especially on weapons that have a lot of rounds through them. |
| You don't want to distort the screw heads. I don't know who decided that was required to "optimally" stake the carrier key. The knurling on the sides of the screw head are there to grip the slight bit of metal that should be displaced into the gap between the carrier key top and the screw head. If you think that you have to distort the screw head, then where do you stop? Tack welding? |
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Which is why I said what I did; a small upset of the screw head is more robust than just pushing key material into the knurling, but even that small amount impacts both how much distortion is done to the key and how stable the key itself if. If you make a small notch in the screw head with the lateral staking we see in the OP's picture, I would think that would indicate "you've done more than enough"...as is "STOP."
You don't want to distort the screw heads. I don't know who decided that was required to "optimally" stake the carrier key. The knurling on the sides of the screw head are there to grip the slight bit of metal that should be displaced into the gap between the carrier key top and the screw head. If you think that you have to distort the screw head, then where do you stop? Tack welding? On the other hand, if you're doing vertical staking, you MUST distort the screw heads to some extent because the knurling doesn't extend all the way to the top of the screw-which is flush with the top of the key. |
| One thing I've never quite understood...with so many pins and detents and such in the AR-15 design, why are the screws holding on the gas key staked like that? Why couldn't they also be designed to be held in place with a detent or a clamp or something that's as capable of keeping them from coming out and much easier to undo? |
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One thing I've never quite understood...with so many pins and detents and such in the AR-15 design, why are the screws holding on the gas key staked like that? Why couldn't they also be designed to be held in place with a detent or a clamp or something that's as capable of keeping them from coming out and much easier to undo? Detents are for things that move regularly. I don't think anyone wants a gas key to move at all. It could be designed to be safety wired in place...but we don't want that either; safety wire is a pain, and frankly it's for things that get "routinely" removed and replaced. |
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On the other hand, if you're doing vertical staking, you MUST distort the screw heads to some extent because the knurling doesn't extend all the way to the top of the screw-which is flush with the top of the key. The fallacy in that line of though is that the metal displaced from the key when vertical staking doesn't extend below the top plane of the key and won't reach the knurling. It most certainly will if done with a center punch. If you're staking with a flat ended cold chisel or the like, you are correct becasue the metal will be displaced only perpendicular to the flat of the chisel. If you HAVE to use a chisel to stake, you need to go all the way across the screw and you will seriously distort the screw head. In this case it woll be more and issue of the screw head coming out to meet the key rather the the other way around as it should be. |
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