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Posted: 4/17/2016 6:07:08 AM EDT
I torqued the castle nut on the buffer tube to 40ft-lb with a armorer's wrench (hooked with a beam torque wrench). I saw a crooked buffer tube and my heart sank; undid the castle nut and saw that the end plate ate through the threading on the tubing. What happened here? Too much torque? Bad parts?
I also noticed that some of the threads were damaged by the teeth on the armorer's wrench. Is this normal? 
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Did you clamp the receiver or the tube? ETA: If the wrench teeth are a little long it can scrape the threads; I've had good luck with the Tapco armorer's wrench. I also like to hold some counter torque on the tube with my hand when cranking on it. I clamp the receiver so the friction from the nut isn't trying to turn the lower on the tube. |
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I've had this happen at least once before. It's because when you were tightening the castle nut, the buffer tube also tried to turn when torque was applied, causing the buffer tube to turn into the metal tab on the backplate.
It's fine, as mentioned just touch it up with a paint pen. What you need to do is try to clamp the lower or extension in a vise(or support the best you can) and when you are putting the final torque on the nut, make sure you grab the buffer tube and hold it firmly so it too does not spin. Then stake it. |
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Those threads are just a but messed up, not ruined. The castle nut should smooth them up a bit - run it on and off a few times and the receiver extension's threads will smooth out nicely. The first (and so far only) extension I messed up this way took several chasing with a threading die to clean it up, but it worked fine afterward.
The key to torquing a castle nut is to get things settled in and ready before you apply the torque. I got all gung ho and carved out two wooden blocks to hold the lower for this, and it worked. But you can also hold the lug on the bottom of the receiver extension and it should do the same thing. As others noted, the tab on the receiver end plate is for indexing, not to hold the receiver extension in place. It is MUCH harder than the receiver extension, so it can and will dig into those threads. Don't give it a chance! Get the extension properly centered and hand tighten the castle nut BEFORE you even think about your torque wrench. |
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You guys were right, it needed a counter torque to keep the tube in place. I cleaned the thread of burrs and had someone hold it down with a stock on. It's looking all beat up now, couldn't lock the teeth firmly into the castle nu, but it's torqued...
I'm not staking it so if it comes loose, I'm using it as an excuse to get a new buffer tube. Thanks for the tip y'all. |
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