View Full Version : Carrier key bolts and staking.
Bill Alexander
08-20-06, 18:08
In the light of the many and varied discussions regarding the does and donts of how to stake the gas key screws, I was mulling over the benefits of lateral staking vs top staking.
Those who are somewhat more high speed than myself seem to be condeming top stakes on the gas key screws, but I have been examining some of my repair records. To date I have manufactured something in the order of 9000 units and every single carrier key was top staked, only a single unit was ever repaired due to a loose gas key and this was traced to the owner removing it. Also we are not talking about 5.56 guns here. The majority of these units are 50 Beowulfs and the rest are 6.5 Grendels.
What prompted me to write this was an odd couple of hours testing at the local range. A rifle was tendered for examination by a rather proud owner, and during the look see I noted that the gas key was staked laterally with a great degree of enthusiasm, problem was the assembly was with import grade screws and you could see the things deforming from the hex drive used to fasten them.
My conclusion from my records is that the lateral staking is ridgid but that in many cases the tensile strength of the fasteners are simply not up to the job. The screws threads deform plastically rather than elastically under load so the tension is not maintained and hence they can be driven undone by the cyclic loads, Heavy staking fixes the problem but not the cause.
My recommendation is that any carrier/key assembly that is intended for heavy use should be installed with premium, certified fasteners, specifically the Holo-Krome 10-32 1/4 type grade 8. These can be easily recognised by a slight knurl at the top and the letters HK rolled into the side of the head. All top surfaces are radiused. Installation should be with a very light lubrication (WD-40 typical) and torqued to 40 inlbs.
These fasteners do cost significantly more than the commom types at nearly 20c each rather than 3c, but are very good insurance. Regardless the staking must be adequate but top stakes are acceptable for long term high usage application.
Bill Alexander
Mr. Alexander excellent point and great post. Thank you for sharing, I myself have come to believe the right screw is more important than the method of staking.
Robb Jensen
08-20-06, 19:23
Anyone know who's screws Brownells is selling? They do have knurling and work well. I've never noticed letters or numbers on them.
I use the Brownells screws when installing new carrier keys and never reuse screws. I also never tighten and restake loose keys (I've been told their usually warped slightly). I always replace a loose key with a new one and use new screws, torque to USMC spec (35-40in lbs) and stake with a MOACKS (Ned Christensen) staking tool before getting this tool I used to use a 1911 front sight staking tool.
Another trick I do, learned from a former USMC 2112 (a good friend of my dad) which works nicely is that I removed the finish of the bottom of the gas key using a medium Arkansas stone. I don't know if this trick squares the bottom of the key or if the removal of the finish there gives a tighter gas seal either way it's works well.
Dave Berryhill
08-21-06, 09:50
Interesting obervation Bill, especially about sub-standard screws. I wonder if loose carrier keys have ever been an issue with the military rifles or if it just exists in the civilian market. I have no data but my guess is that it's just a significant problem for civilian rifles since the military has specifications on the screws used and the protocol has always been to install new screws if the carrier key is removed. You never know what screws have been used on civilain rifles.
Of course if the manufacturer never stakes them to begin with, you're bound to have problems no matter what grade of screws were used..
Do carrier keys ever break at one of the screw holes?
I've seen some staking jobs that look like they were done with bolt cutters and nearly cut the key in half. I always stake the screws front and back (with a punch) rather than on the sides just in case that could be a problem.
Pat_Rogers
08-21-06, 11:00
I start all of my classes now by having the students show me their BCG. The number of unstaked/ poorly staked gas keys is amazing, and running at appx 30% in the open enrollment classes.
We generally don't see this issue in the mil classes because Colt and FN are held to a standard, while the other tier makers apparently do what they wish (or don't do, or do poorly). I don't believe that i have ever seen an unstaked/ fifi staked gas key on any mil gun (again, Colt and FN).
Dave- hope that answers your question. Your comments are dead on.
For those low end makers that can't be bothered to stake the gas keys, the Ned Christiensen MOACKS (look for the SWAT magazine article in the Oct issue on this jewel) works like a charm, and mine gets a lot of use.
Griz- love that- posting while Virginian...I have seen one broken screw while the key was attached, but have not seen a broken gas key.
I have seen some gas keys damaged from making asymmetrical contact with the gas tube.
Bill- thanks for the good info on the screws!
Not all makers build up to a standard, and i am shocked at how many aftermarket guns show up at class with major problems.
As my Dad said- "Buy cheap, buy twice".
It's nice to see posts here that comment on new trends, fads or "issues" that come up regarding parts, methods, etc.
It's especially nice to see these posts by credible people who can actually shed some light on the issue as opposed to simply bringing up "what-ifs" and suppositions...
Posts like this are what set this place apart from other places.
thank you
Joe
I'll post some before and after pics of my LMT BCG that is on it's way back from Gotm4's.
The stake job from the factory was pretty bad so he was gracious enough to hook me up by applying Neds tool to it. As soon as it comes back I'm heading off to the range to zero and break in my new BCM upper.......:D
I have Ned Christiensen's little staking tool and it does an excellent job! I personally stake all CMT BCG's before they leave my shop. They do come staked, but it is poorly done IMHO. I have also contacted the company about this problem.
Generally speaking, the only BCG's that I have found to have a good stake job are FN, LMT, Colt and the ones that I do. If you buy a RRA, BM, Oly, etc make sure to check the stake job.
C4
It's nice to see posts here that comment on new trends, fads or "issues" that come up regarding parts, methods, etc.
It's especially nice to see these posts by credible people who can actually shed some light on the issue as opposed to simply bringing up "what-ifs" and suppositions...
Posts like this are what set this place apart from other places.
thank you
Joe
Joe,
I am glad you that you like the forum. We don't like speculation or "what ifs" on this forum. First hand experience FROM KNOWLEDGEABLE people always works best.
C4
Pat_Rogers
08-22-06, 08:35
Correct Grant. With some of those listed, the stakes are non existed or done with a #2 pencil and a marshmallow hammer.
I am amazed how some companies advertise "mil-spec" this, and "mils-spec" that, yet fail to meet a standard.
I have seen Pat's book of broken gear. Let's just say that there are a whole lot of broken bolts and improperly staked carrier keys from companies that most people regard as a "high end" manufacturer.
C4
OK .. Got my BC back today from GotM4.. (Thanks alot Brother...:D )
and here are the pics I promised. the first pic shows a Bushmaster carrier made in 93-94 time frame with a very good stake job, have 14K rds thru it an no problem. The BC on the bottom is a brand new LMT carrier . The staking job looks kind weak.http://img.photobucket.com/albums/v494/harv24/IMG_1075.jpg
And here is the LMT after Neds Tool got applied to it.....
http://img.photobucket.com/albums/v494/harv24/IMG_1114.jpg
Now my confidence level is Beau Coup high and I can start breaking in this bad boy.
Heavy Metal
08-23-06, 20:11
I have seen Pat's book of broken gear. Let's just say that there are a whole lot of broken bolts and improperly staked carrier keys from companies that most people regard as a "high end" manufacturer.
C4
Now don't snake around who that might be Grant! Lets not go beating around the bush!
Respectfully, I have a quick correction to the above specs Bill stated for the carrier screws in case anyone wants to buy some certified cap screws on their own as I recently have.
The correction is as follows:
#8-32 (not #10-32 as Bill stated)
The rest of Bill's specs were accurate
Razorhunter
02-10-07, 11:53
Just following along in this wonderfully informative thread.
" Ned Christiensen MOACKS Tool" - Where might one pick one of these up??? Must they be purchased directly from Ned himself???
" Ned Christiensen MOACKS Tool" - Where might one pick one of these up??? Must they be purchased directly from Ned himself???
http://www.m-guns.com/tools.php
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