View Full Version : Correct Method of Tightening Castle Nut
What is the correct method of tightening/torquing the castle nut to insure correct alignment of the buffer tube with the lower receiver?
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?
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?
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.
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.
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.
Five_Point_Five_Six
11-11-19, 08:41
Eyeball it, torque it down, stake it, and drive on.
Hold the wrench as perpendicular to the RE and castle nut as possible. I've seen when the wrench isn't 90 degree to the bore, it can put tremendous amount of torque, all localized on the weakest part of the castle nut's wrench notches, the picture below is an example of it.
59591
I mostly tighten, twist the tube while holding the nut, then torque and it ends up straight imo.
That's what I do. Some parts combos don't require any effort, where others have a lot of turn play.
titsonritz
11-11-19, 18:41
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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38-42 ft/lbs
Indeed, we laser engraved it on our JCW (Joint Castle nut Wrench) as a reminder :)
JCW has a 2 lug wrench on one side, and a conventional 3 lug wrench on the other.
59597
jerrysimons
11-12-19, 13:27
Op the only jig I know of for this procedure is the one I now use. Present Arms Gunners mount with both the lower receiver and extension components. It holds both the lower and the receiver extension secure. It is not cheep but neither is the end plate tab gouging out the threads on Vltor A5 extensions using the Geissele Reaction Block, which allows the lower and end plate to rotate from the friction of the castle nut face on the end plate. My OCD disallows me to put up with alignment error or simply snugging a castle nut short of full torque spec, which is not desirable even with staking as threads on the receiver, nut and extension can have more play than the should sometimes.
https://www.brownells.com/gunsmith-tools-supplies/general-gunsmith-tools/bench-blocks/gunner-s-mount-prod58630.aspx
https://www.brownells.com/gunsmith-tools-supplies/general-gunsmith-tools/bench-blocks/ar-15-lower-receiver-repair-block-prod105281.aspx
https://www.brownells.com/gunsmith-tools-supplies/general-gunsmith-tools/bench-blocks/receiver-extension-alignment-block-prod105284.aspx
Without modification the present arms jig is not compatible with Colt lowers that block auto sears in the fire control pocket and is not compatible with lowers using right side bolt catch and releases (LMT MARS-L and LWRC IC). Also some billet lowers might not work.
Im late to the game but install the assembly and using a stock to apply reverse tension when torquing helps a lot. Gooduntite then check and stake. It doesnt take much to hit 40ft/lbs unless your some antifa dweeb.
PS. Anti-Seize on the threads,
titsonritz
11-13-19, 10:50
Im late to the game but install the assembly and using a stock to apply reverse tension when torquing helps a lot. Gooduntite then check and stake. It doesnt take much to hit 40ft/lbs unless your some antifa dweeb.
PS. Anti-Seize on the threads,
This is what I do except I use the grip while the RE is in the reaction block.
ViniVidivici
11-14-19, 20:19
I mostly tighten, twist the tube while holding the nut, then torque and it ends up straight imo.
'Bout what I do. Get behind gun. Eye it. Easy. Get it tight, stake with center punch.
And don't listen to the "blue-loctite-only-crew". Their jive is bunk, yo.
Stake with a center punch.
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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This....is right. I can't imagine one loosening from this torque, with or without a staking.....
Many have seen castle nut loosen even with staking. TM specifies the castle nut to be staked in two places.
Those that don't believe in staking would cite "never happened to me" or "never saw it happen" as reasons, they're not reasons to me, but rather excuses for defending their position. Either it's done correctly, or it's done incorrectly. For a hobby grade AR, one can get away with improperly installed (i.e. non-staked) castle nuts, for everything else, it's a good idea to follow best practice and what Colt, FN, Colt, SOLGW, SIONICS, BCM, etc. do.
https://www.forwardcontrolsdesign.com/Staking-the-castle-nut_ep_64-1.html
Many have seen castle nut loosen even with staking. TM specifies the castle nut to be staked in two places.
I noticed that both of my recent Colt AR purchases had staking in two locations.
This....is right. I can't imagine one loosening from this torque, with or without a staking.....
The correct torque spec is 38-42 foot pounds.
Iraqgunz (Will Larson) was big on "little things" like this, and it irked him that many big companies still don't do it right. It was a polarizing topic whenever it came up on FB, but it shouldn't be.
Some think it unnecessary and mention their decades of gunsmithing experience, that's really inconsequential. Exposure to something does not make a person an expert in the field.
titsonritz
11-19-19, 13:37
This....is right. I can't imagine one loosening from this torque, with or without a staking.....
No it is not, read posts #13 and 14, reference AR TM 9-1005-319-23&P.
ETA: And #23
Many have seen castle nut loosen even with staking. TM specifies the castle nut to be staked in two places.
Those that don't believe in staking would cite "never happened to me" or "never saw it happen" as reasons, they're not reasons to me, but rather excuses for defending their position. Either it's done correctly, or it's done incorrectly. For a hobby grade AR, one can get away with improperly installed (i.e. non-staked) castle nuts, for everything else, it's a good idea to follow best practice and what Colt, FN, Colt, SOLGW, SIONICS, BCM, etc. do.
https://www.forwardcontrolsdesign.com/Staking-the-castle-nut_ep_64-1.html
Excellent write up.
EzGoingKev
11-24-19, 20:38
Indeed, we laser engraved it on our JCW (Joint Castle nut Wrench) as a reminder :)
JCW has a 2 lug wrench on one side, and a conventional 3 lug wrench on the other.
59597
It would be nice if you engraved the center to center distance of the half inch receiver hole and the spanner area so it would make it easier to compensate for the additional length when attaching it to a torque wrench.
As you all know, the fitment between the end plate and the extension along with the rotational torque will turn the extension past the ideal point causing the canting. three things
If possible, try to use an end plate with a nice wide tab to minimize play in the channel of the extension.
Hand tighten the castle nut as tight as possible (spray some MAN on it or use Triactin) and hold the extension turning it counter clockwise while doing so. The extension will appear to be canted to the right at this point. This is observed from the butt end and the stock toe would appear to be to the right (5:45, clock method)
As you tighten, the torque will turn the extension a tad and it will end up at the 6:00 position. You may need to hold the extension or stock to aid in the alignment.
Stock end plates usually are loose fitting causing the cant to be worse than aftermarket ones which usually fit with less lateral play between the tab and channel.
Yes, never seen a staked one loosen but have seen plenty of unstaked ones do so.
It would be nice if you engraved the center to center distance of the half inch receiver hole and the spanner area so it would make it easier to compensate for the additional length when attaching it to a torque wrench.
Do the math, I haven't yet on the above extension but I know by using the Magpul wrench with a torque drops it down to the low 20's, don't have it in front of me but it's 22-23. Remember your torque wrench length will affect this number. I'm guessing that's why it's not listed and it's easily measured or estimated.
https://www.protorquetools.com/formula-to-add-an-adapter-to-a-torque-wrench/
EzGoingKev
11-25-19, 09:45
Do the math, I haven't yet on the above extension but I know by using the Magpul wrench with a torque drops it down to the low 20's, don't have it in front of me but it's 22-23. Remember your torque wrench length will affect this number. I'm guessing that's why it's not listed and it's easily measured or estimated.
https://www.protorquetools.com/formula-to-add-an-adapter-to-a-torque-wrench/
I did not ask for the formula or any of that.
Snap-on engraves it on their torque adapters -
59777
If you are going to engrave info on there you might as well include that too.
We did pay attention to that from the start, which is one of the two reasons it's kept short. The other one is JCW is a dedicated castle nut wrench, it doesn't need to be any longer than it is.
Our conclusion and calculation is the little length it adds, from the torque wrench socket to either the 2 lug wrench or the 3 lug wrench, is so short as to be a non-issue, given the torque range of 38 to 42 which allows ample freedom within the scope. Any shorter than than, we'd risk interference from the torque wrench's head.
We could engrave the distance, but believe most will ignore it, since they won't take the very minor offset into consideration.
If you put the adapter at 90 degrees to the wrench, you don't have to worry about the extension length :cool:
However, from your picture the offset length looks like 1-3/4 inches. So, with a 18 inch long torque wrench set at 38 to 42 ft-lbs, and the adapter set parallel the wrench, the applied torque would be between 42 -46 ft-lbs.
Some torques in the Maintenance Manual include the length of the torque adapter. "Correcting" for the length will result in under torquing.
Eyeball it, torque it down, stake it, and drive on.
This.
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