November 2008 is to my knowledge the newest TM and the first where I've seen the castle nut torque corrected. Took a while.
I had never heard of torquing something to inch pounds until I bought a scar. I bought a pws extension for it and had to torque the barrel fasteners back to 62 inch pounds.
I asked a buddy of mine who owns a body shop and he said he'd never heard of it either until he tried to fix an intake manifold on his daughter's car and the manifold turned out to be plastic.
It called to be tightened to inch pounds and he took it to a mechanic who told him it was easy and loaned him the torque wrench.
I can turn a screwdriver to more force, some people have a complete lack of common sense.
For anybody who might want to download the "latest and greatest" here is the Nov 2008 version.
For anyone further curious, the updated spec for the issue in question is on page 0025-8.
http://kdeguns.com/ar-manual/M4%2016%2023Pchange8.pdf
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I have a inch/pound torque screwdriver that I bought years ago.
If the guy knew that 40 in/lbs was actually 3.3 ft/lbs he might have realized how little torque he was actually putting on the nut.
Some people's kids.... :rolleyes:
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The 1991 version had the incorrect torque spec information. Unfortunately so many years went by until it was corrected in the 2008 manual that the amount of misinformation passed on has created many issues. I truly believe that is why so many people actually started using loctite on the receiver extensions and castle nuts. When in reality if they had used the correct torque specs and a simple stake job then there would be no issues. Heck even Brownells build video claimed the 40 inch pound spec.
I was trained via Colt, who's manuals have always been correct and I was debating with people over this topic for a decade until the 2008 .mil manual hit the scene with the corrections. Hell I had even attempted to use common sense in explaining that 40 inch lbs is only 3.33 foot pounds, which is basically hand tight. I had some aerospace geek claiming that the aluminum receiver / receiver extension could NEVER possibly take the torque of the steel castle nut up to 38 ft lbs. :rolleyes: I believe that there was even a thread or two here about the topic. In reality most people who do this often or for a living don't even use a torque wrench anyway. :)
Yeah, it's not all that necessary if you know what right feels like. But, there is a spec for torque and I have the tools to get it exactly right. So I do. No reason not to other than to save time. This forum is constantly preaching that AR's aren't "Leggos," which is absolutely true. Getting little things right like hitting a 4 ft/lb window for castle nut torque is what separates a shitty home build (even though the components may be good) from a properly assembled rifle.
I wouldn't go so far as to say doing it by feel is "cutting corners" if you've done it hundreds of times, but I don't think anybody can feel the difference between 36 and 38 foot pounds. I'll take the few extra minutes to get it exact.
Can you exceed 38 ft/lbs with a 6" long castle nut wrench?
80 pounds of force on the end will do just that. You have to crank on it but I would say it is possible.