View Full Version : Build a BCG Like an Idiot? Surprisingly Useful Article from TFB
Tzintzuntzan
12-07-16, 16:05
Surprised I saw this especially considering the source.
http://www.thefirearmblog.com/blog/2016/12/07/build-ar-bcg-like-idiot-rock-river-arms/
Glad to see that good information is starting to become more widely spread about how shit certain companies procedures are for building new rifles. Maybe it will make a change but it doesn't seem like this comment will have too strong an impact on the industry, considering the comments section for the article.
Well, the writer did attend William Larson's class, which is a good thing.
Tzintzuntzan
12-07-16, 16:55
Very true hopefully more people who want to build ARs both professionally and for themselves seek training by qualified individuals instead of the first WikiHow article they can get on Google. Or some random gunshop commando who puts a gas block at a mid length position when the barrel has the gas port at 7". That was a surprising thread.
The derp has already begun to leak....
The derp has already begun to leak....
When will ya'll offer armorers courses in the VA/NC/TN area?
But but but my rra is just as good as...
What is the proper to install an extractor spring?
Tzintzuntzan
12-07-16, 22:12
Just noticed that they changed the original title. I guess their comment section didn't like the old one. Can't wait to have an Iraqgunz course near me either. One of these years right? :D
I actually do believe in staggering gas rings. Not for function but for assembly, as I've seen the end of one ring jammed into the gap of another.
RobertTheTexan
12-07-16, 22:42
What is the proper to install an extractor spring?
Apparently not the way the RRA dude did it.
I would prefer not to have to build a BCG, I prefer to buy quality BCGs and have spares.
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The point isn't to build anything. All the stuff he did are also common repairs that someone may need to make. I have had to replace numerous carrier keys over the years due to blown primers, Q-tips stuck inside, crappy stakings, sheared screws, etc..
Apparently not the way the RRA dude did it.
I would prefer not to have to build a BCG, I prefer to buy quality BCGs and have spares.
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RobertTheTexan
12-08-16, 00:57
The point isn't to build anything. All the stuff he did are also common repairs that someone may need to make. I have had to replace numerous carrier keys over the years due to blown primers, Q-tips stuck inside, crappy stakings, sheared screws, etc..
That's a good way to look at it - potential repairs.
I could probably do some, maybe most of the steps in the video, I've done some basic repair/replacements like replacing gas rings, the extractor spring and o-ring that came in a SOPMOD kit that I keep in my spares.
I think I'd rather get some training and KNOW that I know what I'm doing rather than do the whole "Hope for the best, but plan for the mess". That may not be the saying but it sure sounds applicable.
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Robert -
I noticed several times he mentioned something along the lines of 'to do this at home' which, along with a couple of other items made me believe the clip was not necessary 'build a bolt carrier group the factory way' but rather 'build a bolt carrier group the minimalist way.' I'm not sure that it was a good idea for a company to produce such a clip.
Since the article commented on the torque - he said it should be done with a torque wrench and then added how to do it with the allen wrenches. 55-60 inch pounds is the norm, 70 inch pounds isn't going to harm anything in my experience. We are talking less than one foot pound of torque difference here, not cheater bar tightness.
People often refer to the Armalite Tech Bulletin #47, here that bulletin:
Technical Note 47: Increased Carrier Key Torque
For years, veteran ArmaLiteŽ assemblers have tightened carrier keys using a simple Allen wrench. This process has been successful.
As we added employees we decided to use calibrated torque wrenches to assure that we secure the key screws to the proper level. The government standard for carrier key torque is 35 to 40 inch pounds, and we secured torque wrenches set to that value. We then noticed an INCREASE in loose carrier keys. It turns out that we had tightened carrier key screws better without the wrench than with it.
The problem is that the government torque values shown in maintenance manuals are too low.
We have examined the engineering data related to the screw itself, and have increased torque to 55 inch pounds to improve carrier key tightness. We recommend that all AR owners make sure that their carrier key screws are secured to this level, especially if their rifles sometimes shows signs of weak or slow cycling.
If your AR "short strokes," clean the underside of the carrier key and tighten both screws to 55 to 60 inch pounds. Tighten the front screw first. If your rifle isn't short stroking, just make sure that the screws are tight and restake if needed.
MARK A. WESTROM
President
Additionally, the ejector spring. 'Jake' mentioned it should snap in. He then said if it didn't you could use pliers, cautioning that you could harm the spring if you used too much force.
The article mentioned the stakes weren't good enough, IDK how they could know, IIRC the video never showed the finished stakes (although I could be wrong).
It is nice to have the content of the Brownell's AR tool catalog on your bench, most of us can't afford that.
I'll end by repeating something I said earlier _ RRA should have known they would get creamed by every guy on the internet who has read about building AR's.
It's real simple. Go look at the stakings in an RRA. I can tell you for a fact that key wasn't staked as have most of the professionals who have seen it.
Robert -
I noticed several times he mentioned something along the lines of 'to do this at home' which, along with a couple of other items made me believe the clip was not necessary 'build a bolt carrier group the factory way' but rather 'build a bolt carrier group the minimalist way.' I'm not sure that it was a good idea for a company to produce such a clip.
Since the article commented on the torque - he said it should be done with a torque wrench and then added how to do it with the allen wrenches. 55-60 inch pounds is the norm, 70 inch pounds isn't going to harm anything in my experience. We are talking less than one foot pound of torque difference here, not cheater bar tightness.
People often refer to the Armalite Tech Bulletin #47, here that bulletin:
Technical Note 47: Increased Carrier Key Torque
For years, veteran ArmaLiteŽ assemblers have tightened carrier keys using a simple Allen wrench. This process has been successful.
As we added employees we decided to use calibrated torque wrenches to assure that we secure the key screws to the proper level. The government standard for carrier key torque is 35 to 40 inch pounds, and we secured torque wrenches set to that value. We then noticed an INCREASE in loose carrier keys. It turns out that we had tightened carrier key screws better without the wrench than with it.
The problem is that the government torque values shown in maintenance manuals are too low.
We have examined the engineering data related to the screw itself, and have increased torque to 55 inch pounds to improve carrier key tightness. We recommend that all AR owners make sure that their carrier key screws are secured to this level, especially if their rifles sometimes shows signs of weak or slow cycling.
If your AR "short strokes," clean the underside of the carrier key and tighten both screws to 55 to 60 inch pounds. Tighten the front screw first. If your rifle isn't short stroking, just make sure that the screws are tight and restake if needed.
MARK A. WESTROM
President
Additionally, the ejector spring. 'Jake' mentioned it should snap in. He then said if it didn't you could use pliers, cautioning that you could harm the spring if you used too much force.
The article mentioned the stakes weren't good enough, IDK how they could know, IIRC the video never showed the finished stakes (although I could be wrong).
It is nice to have the content of the Brownell's AR tool catalog on your bench, most of us can't afford that.
I'll end by repeating something I said earlier _ RRA should have known they would get creamed by every guy on the internet who has read about building AR's.
The point isn't to build anything. All the stuff he did are also common repairs that someone may need to make. I have had to replace numerous carrier keys over the years due to blown primers, Q-tips stuck inside, crappy stakings, sheared screws, etc..
Have you ever seen a properly torqued gas-key come loose (Youngs)?
Why must a gas-key screw be staked, when we LUBE the barrel nut?
My questions are facetious, but also genuine. If the barrel nut doesn't walk off, then why should the gas-key set screws? Have you or anyone ever seen properly torqued gas-key set screws do this?
Have you ever seen a properly torqued gas-key come loose (Youngs)?
Why must a gas-key screw be staked, when we LUBE the barrel nut?
My questions are facetious, but also genuine. If the barrel nut doesn't walk off, then why should the gas-key set screws? Have you or anyone ever seen properly torqued gas-key set screws do this?
I think if you think about the size, dynamics, design, and differences in stress that each are under, for about one nanosecond longer, the answer is quite obvious.
I think if you think about the size, dynamics, design, and differences in stress that each are under, for about one nanosecond longer, the answer is quite obvious.
Ever seen a properly torqued A2 flashhider come loose? what kind of forces do you think it's under?
Better yet...have you ever seen a properly torqued gas-key come loose?
You're kidding right? I have seen it so many times it's not even funny. The torque value is so low, it makes the staking even more important. Barrel nuts are torqued in ft./lbs. not in./lbs. When done correctly they will not loosen.
Lastly, what Ryno stated pretty much sums it up.
Have you ever seen a properly torqued gas-key come loose (Youngs)?
Why must a gas-key screw be staked, when we LUBE the barrel nut?
My questions are facetious, but also genuine. If the barrel nut doesn't walk off, then why should the gas-key set screws? Have you or anyone ever seen properly torqued gas-key set screws do this?
Ok Jake from Rock River....she sounds hideous.
Seriously though, I could't watch that whole video.
IG needs to hurry up and get over to MI and start spreading the gospel in my AO!
Ever seen a properly torqued A2 flashhider come loose? what kind of forces do you think it's under?
Better yet...have you ever seen a properly torqued gas-key come loose?
Ryno has a very valid point. Are you talking about the crush washer under the A2? Again think about the design, function, and actual forces at work, and these questions will answer themselves.
I believe the target audience of the video was the hobbyist who has limited hand tools and not professional gunsmiths who do this for a living. It's nice to have specialty tools if you perform maintenance with great frequency.
I attended an armorer school sponsored by Armalite in 2004 and we were told 55 inch pounds was the preferred torque for the bolt carrier key screws. If a torque wrench was not available, it was suggested you press the end of the allen wrench with your fingertips until you have 20-25 degrees deflection.
We did not have access to a staking tool and used a prick punch to perform the staking operation in accordance with Army TM 9-1005-319-23&P page 3-28. It may not look pretty, but should secure the bolt carrier key screws if properly done.
We were told that the extractor spring and extractor pin should be installed by hand. That is covered in Army TM 9-1005-319-23&P on page 2-42. If you have to force any of the parts together with tools, something needs attention before proceeding.
Staggering gas rings is covered in Army TM 9-1005-319-23&P on page 2-40. It may not be necessary, but I still do it according to the tech manual.
If someone has limited funds, my suggestion would be to purchase a good set of roll pin punches before anything else. I strongly suggest purchasing the punches from Brownells or another reputable company, because I have measured hardware store punches that were oversize, i.e. a 1/16" punch being 0.068" and a 1/8" punch being 0.132". You can make a mess of things in short order with oversize punches.
I am a bit curious why "Jake" did not use any lubricant during assembly.
Why must a gas-key screw be staked, when we LUBE the barrel nut?
This question shows your lack of knowledge. Staking a bolt/screw has nothing to do with lubricating anything.
Lubricating a mating surface is entirely different than lubricating a reciprocating mechanism.
If the barrel nut doesn't walk off, then why should the gas-key set screws?
12 in/lbs of torque = 1 ft/lb of torque.
Gas keys staked to 58 in/lbs = 4.83 ft/lbs
A barrel nut gets torqued between 30-80 ft/lbs
This question shows your lack of knowledge. Staking a bolt/screw has nothing to do with lubricating anything.
Lubricating a mating surface is entirely different than lubricating a reciprocating mechanism.
12 in/lbs of torque = 1 ft/lb of torque.
Gas keys staked to 58 in/lbs = 4.83 ft/lbs
A barrel nut gets torqued between 30-80 ft/lbs
Before I start this I'll make this assertion - I am a staking adherent. Having said that I do think sometimes we go overboard on the whole staking thing.
For years my family raced speedway go karts. The engines we used were Briggs Raptors (5 horse lawn flathead mower engines). In the kart the engine is alongside the driver. They turned 5,000 to 6,000rpm flat out most of every race. Every torque value on that engine, save the flywheel nut, is in inch pounds - the head bolts are the highest @ 150 inch pounds (12.5 footpounds) the rod bolts @ 110.
No washers, no staking. Never had one come apart - never seen one come apart aside from rods going through blocks.
I guess I'm lucky that any of us are alive.
Every torque value on that engine, save the flywheel nut, is in inch pounds - the head bolts are the highest @ 150 inch pounds (12.5 footpounds) the rod bolts @ 110.
No washers, no staking. Never had one come apart - never seen one come apart aside from rods going through blocks.
You, also, are missing the point. WS6 was comparing a machine screw torque value to a barrel nut torque value that could potentially be 20 times higher. The gas key screws have a specific torque value in in/lbs for a reason, just as the barrel nut has a specific torque value in ft/lbs.
Mil-Spec grease is specifically Aeroshell 64 (33MS), so that's what I use.
The upper receiver can handle a standard nut at 80 ft/lbs, but my Geissele Barrel Nut instructions said 40 ft/lbs, so that is what I use.
The bolts on the SMR Mk8 handguard have a torque value of no greater than 8 ft/lbs, so that's what I use.
I'm not a stickler for telling people what they should or should not do, but if someone tells another person that an improperly staked BCG is okay, they are wrong and I will correct them. Some people put together a rifle with hand tools, and that's fine, but it doesn't mean it is the correct way to do it and it doesn't mean they should be giving advice.
You, also, are missing the point.
I'm not a stickler for telling people what they should or should not do, but if someone tells another person that an improperly staked BCG is okay, they are wrong and I will correct them. Some people put together a rifle with hand tools, and that's fine, but it doesn't mean it is the correct way to do it and it doesn't mean they should be giving advice.
By this time the original point is so far out in left field that I'm pretty sure we've lost sight of it. I am pretty sure that one of the intents of the AR design was to make it easily assembled and maintained without a lot of specialized tools.
The proper torque - as I tried to illustrate with my engine example - SHOULD hold the parts together. The stakes on the carrier key are a fail safe to keep the bolts from vibrating loose and to serve as an indicator that the bolt has moved.
As I mentioned, I often use a staking tool. But I've also worked on weapons that use stakes to actually hold key components in place. The standard there is 'use a punch to move enough metal to hold the part in place.' There isn't a lot of discussion in those circles beyond that. Sure there are anvils and pliers made to stake 870 latches, and 1911 plunger tubes, but much like the TM for the AR, the standard tool is a punch.
I merely think we go overboard with our criticism of such things as staking. Look at page 70 in The Black Rifle those stakes wouldn't have passed muster here. Likewise page 3-28 in the TM as noted above.
At the end of the day it is no big deal, as long as the stake does as intended.
Actually you would be wrong. There is nothing wrong with a Field Staking. In fact, I did one recently in my class because it was a Young Manuf. BCG and we were concerned about chrome cracking. That said, when there is a tool that will replicate a correct OEM staking and is readily available it makes little sense to not have one.
One could also buy a correct one from the start which would help quite a bit. Considering the cost of a MOACKS and the amount of money that many AR owners simply throw away, it makes little sense not to get one.
42857
By this time the original point is so far out in left field that I'm pretty sure we've lost sight of it. I am pretty sure that one of the intents of the AR design was to make it easily assembled and maintained without a lot of specialized tools.
The proper torque - as I tried to illustrate with my engine example - SHOULD hold the parts together. The stakes on the carrier key are a fail safe to keep the bolts from vibrating loose and to serve as an indicator that the bolt has moved.
As I mentioned, I often use a staking tool. But I've also worked on weapons that use stakes to actually hold key components in place. The standard there is 'use a punch to move enough metal to hold the part in place.' There isn't a lot of discussion in those circles beyond that. Sure there are anvils and pliers made to stake 870 latches, and 1911 plunger tubes, but much like the TM for the AR, the standard tool is a punch.
I merely think we go overboard with our criticism of such things as staking. Look at page 70 in The Black Rifle those stakes wouldn't have passed muster here. Likewise page 3-28 in the TM as noted above.
At the end of the day it is no big deal, as long as the stake does as intended.
Inkslinger
12-13-16, 20:49
Have you ever seen a properly torqued gas-key come loose (Youngs)?
Why must a gas-key screw be staked, when we LUBE the barrel nut?
My questions are facetious, but also genuine. If the barrel nut doesn't walk off, then why should the gas-key set screws? Have you or anyone ever seen properly torqued gas-key set screws do this?
Do you think the gas tube and its relation to the barrel nut help prevent movement of the barrel nut?
No. The gas tube will prevent the barrel nut from coming off but not from loosening. If it's loose your rifle is almost uselessly inaccurate.
Inkslinger
12-15-16, 16:01
No. The gas tube will prevent the barrel nut from coming off but not from loosening. If it's loose your rifle is almost uselessly inaccurate.
I mean on a properly torqued barrel nut. Would the gas tube only allow it to move so far in its path to becoming loose. I mean like a cotter pin through a castle nut or safety wire.
I mean on a properly torqued barrel nut. Would the gas tube only allow it to move so far in its path to becoming loose. I mean like a cotter pin through a castle nut or safety wire.
I think that is what Todd K said. A mill-spec barrel nut has 20 splines, so there is a potential movement of 18 degrees from spline to spline. Of course tube itself would take up much of that space, so let's say movement of between 4 to 6 degrees, or 1/60th of a turn. Unknown what the torque value would be. ALG barrel nuts have 8 splines - so each one is 45 degrees. As close as I can figure if you use their wrench correctly it goes from hand tight to proper torque in about 15 degrees.
So I'd guess that a GI barrel nut would still be a little more than hand tight. Unknown what it would do to accuracy. I have a rifle completed except for the barrel, the ALG tube I looked at goes on that rifle. I will try to remember to take it to the range, sight it in, then loosen the barrel nut to hand tight, check headspace with a field gauge then fire a couple rounds, checking headspace with the field gauge between each one. That should allow the barrel to loosen up from its fully torqued position.
It is going to have to be a little warmer before I do that, though.
Everybody knows that I'm technically unaware about many mechanical AR requirements so maybe I can ask: why not just put the muscle to the carrier screws and then stake them? Why the torque spec? Too, does anybody use Loctite on these screws as a backup measure? If I were going into an uninhabited wilderness(I'm not), I'd be tempted to have the carrier key silver soldered in place in addition to staking. Is this ever done?
Everybody knows that I'm technically unaware about many mechanical AR requirements so maybe I can ask: why not just put the muscle to the carrier screws and then stake them? Why the torque spec? Too, does anybody use Loctite on these screws as a backup measure? If I were going into an uninhabited wilderness(I'm not), I'd be tempted to have the carrier key silver soldered in place in addition to staking. Is this ever done?
Looking at the allen head machine screws and the carrier key, I would say the the easy answer would be once torqued in place to set the assembled carrier into a good mill/drill press vise and carefully angle drill from the interior of the socket head out, then insert a roll pin making sure the end doesn't protrude beyond the carrier key. Would not move. Downside is that the bolts would be single use - doubt that they would torque to the exact same position.
Way too much effort though - torque and stake; or, red loctite, torque and stake. Take an allen wrench/hex key with you into the woods in case they work loose.
Everybody knows that I'm technically unaware about many mechanical AR requirements so maybe I can ask: why not just put the muscle to the carrier screws and then stake them? Why the torque spec? Too, does anybody use Loctite on these screws as a backup measure? If I were going into an uninhabited wilderness(I'm not), I'd be tempted to have the carrier key silver soldered in place in addition to staking. Is this ever done?
I don't know anyone locally who uses thread locker. We just torque the screws and stake them using the field staking technique. Iraqgunz has a good photo of the end result in post # 27.
Everybody knows that I'm technically unaware about many mechanical AR requirements so maybe I can ask: why not just put the muscle to the carrier screws and then stake them? Why the torque spec? Too, does anybody use Loctite on these screws as a backup measure? If I were going into an uninhabited wilderness(I'm not), I'd be tempted to have the carrier key silver soldered in place in addition to staking. Is this ever done?
If you don't have a good feel for torquing fasteners, you'll over torque the gas key fasteners and the heads will eventually break off
Looking at the allen head machine screws and the carrier key, I would say the the easy answer would be once torqued in place to set the assembled carrier into a good mill/drill press vise and carefully angle drill from the interior of the socket head out, then insert a roll pin making sure the end doesn't protrude beyond the carrier key. Would not move. Downside is that the bolts would be single use - doubt that they would torque to the exact same position.
Way too much effort though - torque and stake; or, red loctite, torque and stake. Take an allen wrench/hex key with you into the woods in case they work loose.
How would you keep the roll pins from working their way out? If you're gonna drill the heads of the fasteners, use lockwire. Really, done right, staking is plenty good
How would you keep the roll pins from working their way out? If you're gonna drill the heads of the fasteners, use lockwire. Really, done right, staking is plenty good
Roll pins are spring steel and actually slightly larger than the hole they are sized to fit. They usually have slightly chamfered ends to start them into the hole, once they are installed spring tension keeps them in place.
I actually thought of that, I am a safety wiring fool, my safety wire pliers are the only piece of Snap-On equipment I own. Everything that can possible fall off a Speedway Kart has to be safety wired - ballast, header bolts, axle nuts, steering components, etc. Problem with safety wiring the carrier key is that their is no room for the wire ties.
I agree with you on the torquing and staking, my response was in answering williejc's post.
I have seen several M4's that the barrel nut was not torqued correctly. The gas tube did not keep them from loosening enough to become basically useless.
The torque spec is to keep you from breaking the bolt head off. Tighter is not always better.
Thread locker will just make it harder to repair, if the bolt breaks and you need to remove what's left.
I have seen several M4's that the barrel nut was not torqued correctly. The gas tube did not keep them from loosening enough to become basically useless.
Were the problems accuracy or function? Did the gas tube displace enough to stop the bolt carrier?
The torque spec is to keep you from breaking the bolt head off. Tighter is not always better.
Totally agree, but I think the torque values on the rifle aren't that great. In the case of the carrier key we are talking inch pounds on Grade 8 socket head machine screws. According to Fastenal, grade 8 tensile strength is 150,000 PSI minimum. I'm thinking 20 inch pounds isn't going to make or break the deal.
Thread locker will just make it harder to repair, if the bolt breaks and you need to remove what's left.
Yep, when I suggested red loctite it was in response to williejc's EOTWAWKI scenario.
Wandering zero on most of multiple inches at 25M. No failures to function.
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