What is the correct method of tightening/torquing the castle nut to insure correct alignment of the buffer tube with the lower receiver?
What is the correct method of tightening/torquing the castle nut to insure correct alignment of the buffer tube with the lower receiver?
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Screw the buffer tube in until it holds the spring retainer pin down by the shoulder (ie: the small pin sticks up and catches the buffer spring.) Function test by using a punch to press the pin down, releasing the buffer spring. Snug the castle nut against the end plate, and stake with a spring loaded centerpunch.
Google up "AR 15 receiver assembly instructions" and you'll get plenty of hits for assembly instructions adhering to standard specs.
Without a jig there is a little trial and error as far as alignment goes.
Torque spec is 32-40 ft/lbs
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I've kind of given up in life, as far as this goes. As long as it is within 5 degrees, this is an area where I just drive on.
My current approach is to secure the buffer tube in a Geissele reaction block and torque the castle nut with a FCD castle nut wrench. Keeping the buffer tube lined up correctly with the lower receiver while torquing the castle nut is the key. The buffer tube cannot move in the reaction block but the receiver and endplate tab can rotate out of the groove in the buffer tube if not held secure. What method is recommended to maintain correct alignment to reach the proper torque value?
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With my set up you could get it lined up as you want, tilt the reaction block 'forward' in the vise and then turn the vise (to the right in my case) until the pistol grip contacts the edge of the bench. Then lock the vise down tight and go to town. I have an itty-bitty cheater bar that hasn't bent the base lock-down pin yet in other uses.
This is not the way I do it - I assemble, get everything the way I want, place it it reaction block and tighten the castle nut just a little past snug. I mark dead-center bottom on the castle nut and then disassemble. Drill and tap the castle nut (6-32 or 8-32 - whichever one I have a 1/8" knurled cup set-screw for). Reassemble, snug till set-screw hole is BDC, then using red loctite snug the st-screw.
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I mostly tighten, twist the tube while holding the nut, then torque and it ends up straight imo.
A jig is the best wa. Second best would be a vise block like the one Geissele makes, that holds the buffer tube instead of the lower, as it's easier to hold the lower in line while tightening than the tube.
If all you have is a magwell type vise block, it can help to slip a stock onto the tube while tightening the castle nut. It makes it easier to see when everything is lined up and gives you some extra leverage on the tube to help keep everything straight.
Last edited by Tx_Aggie; 11-11-19 at 08:25.
I hold the extension with soft jaws in a vice on the flat walls of the bottom.
I eyeball it, hold it, tighten it, throw the stock/brace on (eyeball again) and stake it.
Not always perfect, but it's close enough that it doesn't trigger OCD.
Last edited by RMiller; 11-11-19 at 08:42.
Eyeball it, torque it down, stake it, and drive on.
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