Just how much of a problem, if it is a problem, is it likely to be if the staking of a gas key cracks the key’s metal? I ask because I purchased a BCG that has cracking at all four stake points.
If there is a potential for bits to come loose inside, I can see that being a problem akin to having a popped primer. And I suppose it calls into question how secure the gas key screws really are.
But I don’t really know how liable the cracked metal is to start giving up pieces.
Somes pics would probably help.
there’s a thread about this on TOS… seems like a famous manufacturer used MIM gas keys…hence the cracking on stacking points
Kind of hard to take a good picture with what I have:
Take a round jewelers file and radius the crack area and you will be fine.
THAT…, is a big problem if it were mine, cracks in a BCG gas key can only lead to the cracks eventually growing and one day a minor KaaBoom !!
if it were mine i would go for a replacement or $$$$ returned, JFYI i have 4 half circle Colt carriers for sale, two never used and two slightly used, if interested, PM me
Yeah! I read a comment about LMT using MIM gas keys. WTF???
Once a crack is radiused out, it no longer exists and will absolutely not promote further cracking. The NRC, EPRI, and ASNT all agree that this true, and I sure bet they do more testing for my nuclear reactor and associated piping systems and it’s weld conditions than Colt or LMT does on a gas key. Not to mention that if our material fails… thousands die or are evacuated. If a gas key fails, one paper plate lives, or one soldier may die. Who do you think knows more about meterial failure analysis?
I would bet my next pay check that a smoothly radiused area where that crack once was… will forever end the issue.
If a crack like (linear flaw) is detected on any pipe system the area must be ground out and radiused to remove any stress risers created at the tips (extents) of the crack. This process, depending on severity of base material removed, will allow the part to remain in service and also remain on a standard inspection interval. No augmented examinations would be required.
That area is not in a load bearing area of the key, and to radius that small and isolated area that is above the load bearing zone effected by the clamping force (compressional forces that seal the key) will have zero effect on the parts expected performance or life.
You can feel free to toss it out and get a new one, but it is not something you need to do.
All that said, leaving a stress riser will promote propagation of the flaw and overall failure of the part.
Is the round mold mark between the bolts indicative of the key being MIM?
WHAT!!! That is just displaced metal from the staking process…That is NOT going to cause crack promotion into the key…
I have seen LMT, BCM, Larue and even a Colt carrier just like that. Just pound down the high spot, no need to file.
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Yeap…Thats exactly what I did with the one I have thats cracked at the stake.The main reason I did it was to knock the sharp edges down that had actually pulled a chunk of meat out of a finger.The gas keys are very hard and practically dulled a standard hobby type file.Had to use a diamond file and a wet hone to accomplish the task.
Gota couple thousand rounds of ammo through the LMT carrier/gas key in question with no issues.
Yeap apparently so.At least based on what Ive read on the subject of MIM.
The picture shown does not look like a crack to me. I wouldn’t worry about the key pictured at all.
Radiusing the end of a crack does not mean the problem is over, it means you’ve done all you can, and you hope the problem is over. I’m a toolmaker, I’ve dealt with cracks.
Mark15
Yeah this has become a hot topic on TOS and most there think it is a horrible flaw and that it may ruin your gun and that LMT has cut corners. I call BS big time for 2 reasons.
Has LMT ever put out an inferior product or any product without testing the hell out of it. . . . . Nope.
A MIM product like that actually is slightly stronger than a machined product if done correctly and because of it the medal is not as soft. When you try to stake it you take a very small amount of metal and displace it thus stretching it. Since it is not as soft as the machined keys it tends to form a VERY TINY crack in it at the thinest and weakest point. However since it is as strong as it is it is not going to break of any little chunk and ruin your rifle. Now, if each stake was cracked in 2 places then I would worry.
I agree with taking a small file to the crack as sort of a preventative measure if you feel inclined to do so. I have one of the new LMT BCG’s and inspected it and found 2 of the 4 have that vry tiny hairline crack, but I am not worried one bit. After all, they have been out for over 8 months now I believe and not one incident of failure has occured and if it had, it would have been all over this and other sites.
A MIM gas key might not be an issue but why bother when then are standard production alternatives that are proven?
Do you have any data on this? I’m no expert, but this is pretty contradictory to just about everything which I have read and experienced with MIM.
Well I guess I should keep a eye ball peeled on the key staking in this case.The gas key on mine has three seperate cracks at each stake.Seen some pictures of others that were the same way here on the forum.Best way to describe it is that there is a crack at about 10 o’clock,12 o’clock and 2 o’clock at each stake.Roughly.
Appears the material fractured at the points where it was displaced,including at the base…Again the metal is extremely hard and I think is the root cause of the cracks.I do believe that if the screws were removed the metal at the stakes would probably break away looking at the cracks and the material displaced.Otherwise I think its retained against the screws from being folded in at that point.
The hardness of the part is probably how LMT got around not using hard chrome on the key bores as well.
I had my boxers all wadded up over the non chromed key bore and possible MIM sometime back…Im not going to repeat it in this case.
Personally Im just going to run the gas key until I see an issue,and then LMT can deal with it.Otherwise I’ll replace it with a BCM gas key when the gas tube needs to be replaced from wear and tear of use.
I would have to agree. Radiusing the crack just takes out the stress risers. It reduces the chance that the crack/new cracks will propagate. It doesn’t guarantee that no new cracks will form.
MMcfpd,
Is your BCG an LMT, or some other brand? If an LMT, I bet if you contact them with your concerns, they will be responsive to you. If LMT is making their gas keys by MIM now, I expect they would appreciate the feedback, and perhaps they will even replace it for you if it proves to be substandard.