Good evening, all.

I was torqueing down a Geissele MK4 barrel nut onto a BCM M4 stripped upper with plenty of Aeroshell 33ms grease applied. The barrel indexing pin was properly indexed and flush against the receiver inside the index pin channel before I began torqueing. I was using a Midwest Industries reaction rod in a bolted-down vise to stabilize everything.

Admittedly, the torque wrench I was using was not high quality. As I was torqueing up to 40 foot lbs (or so I thought), the knob on the barrel nut wrench sheared clean off. I had the barrel nut hand-tight, and then the torque wrench rotated it roughly an additional 70 degrees when the wrench broke. Based on the videos I've watched of folks torqueing down these barrel nuts to 40 lbs, it seemed like mine was taking wayyy too long to hit 40 lbs, then it busted. The torque wrench definitely never clicked.


This pic shows how close the barrel nut is to the receiver. Would this normally sit flush if it was properly torqued (or over-torqued)?


The slot for the barrel nut wrench nub doesn't seem deformed, just a little marred up.


The barrel nut wrench.

I'm going to get a much better torque wrench and see how much torque it takes to pop this thing off. I'm concerned that I may have way over-torqued and damaged the upper? I cannot see any cracks anywhere, it is not warped or anything like that, and I would think that the barrel nut wrench slot would be deformed if I seriously over-torqued. What do you all think?

Edit: Originally thought I rotated it approx. 90 degrees, but approx. 70 degrees is more accurate after looking at where I started torqueing to where it broke

Pics don't appear

Looks and sounds like you over did it. I’d vote the wrench took the only damage.

OP’s pics:

Pics don't work and try not to use chicom torque wrenches.

Slide the handguard on and see how it fits.  You should have it plenty tight enough

Deleted due to double-reply

Thank you for re-posting my pics. I think you're probably right about the wrench being the only thing damaged. The feed ramps are lining up perfectly with the barrel extension, so that tells me the index pin channel isn't deformed. Won't know for sure until I can get another wrench and remove the nut to inspect the threads and receiver.

Do you really think that is necessary?  Mil nuts spec to 80# and I've exceeded that by a hair getting a clean slot, without issue.  I highly doubt you could have done any damage without knowing.  You really have to lean on it.

I agree here. The picture of that wrench makes it look like it was well-used as well, the galling on the end is questionable. I'm betting it was a tool failure, and your current torque on the barrel nut is fine.

Geissele specs the MK4 nut at 40 ft-lbs without a listed range. They then go on to state that experienced builders can install it without a torque wrench, so there is an implied range. If someone's not used to the feel of torque values, it could be over-torqued/damaged. Figure out your torque wrench situation, set it to 40 ft-lbs, put a socket on it, clamp the socket in a vise and get a feel for what 40 ft-lbs feels like. That might help you determine if you have an issue. Removing it might be a one way trip to a new nut and/or (unlikely) upper. If I was that concerned about it, I'd just use a strap wrench and not worry about the Geissele wrench. Probably should ask what clamping method you were using.
Edit: saw the MI URR

90 degrees past seated seems like a lot more torque than 40ft-lbs with standard AR upper threads.

It's definitely reassuring to hear all this. But I'm a knucklehead so I basically was leaning on it when the wrench failed - my concern is that it may be grossly over-torqued, which I believe can cause various issues in future.





Good recommendation - I'll get a feel for what 40 foot pounds feels like.

So you think that removing it would have a higher potential for causing damage than leaving it over-torqued and shooting it? Not being rhetorical - I'm asking because I honestly don't know.

If I were you I would slide the handguard on and tighten it down and go shoot it. No harm will be done by that.  Those threads are tougher than you are giving them credit for.  The nut looks straight, if it is off even a little the handguard will show it.  If you have ever knocked loose a PSA nut you'd swear that some of those must be tightened well past the number.

Maybe go to Geissele's industry page here and cross-post and contact Geissele directly.  I'll bet they will send you a new wrench.  Then back off and start over with a known good torque wrench.  Cost is not necessarily a good indicator of accuracy.  For instance, the Harbor Freight ones are almost as accurate as Snap-On in comparison tests.  

Also, when using these type barrel nut wrenches, be sure to put the "wrench" on the end of torque wrench at a 90 degree angle rather than straight ahead. Putting it straight ahead increases the effective lever length and will result in over torquing in relationship to the indicated reading.  The Geissele barrel nut wrench does have a slight angle offset even when installed at 90 degrees, but it is too small to be concerned about.

Got it. I actually have read other posts where folks busted their wrenches from trying to remove the barrel nut from PSA builds, so you're definitely right in saying my upper is probably fine. I much appreciate the input.



Good idea - from everyone's input, it sounds like the upper is almost certainly fine. I'll check in with Geissele. And yes, I had the wrench at a 90 degree angle, and thanks for the video. I should have been much more conscious of realizing that the wrench was probably exceeding 40 ft lbs.

Food for thought if replacing the torque wrench:

Agree it’s fine. However, the fit between the rail and nut is VERY tight… like 0.0005” clearance, if that.

OP may meet to dress the area if the aluminum has deformed in the slightest bit. If it becomes a project, may want to get a new nut and start from scratch.

Some manufacturers never fail to impress!

Yes, agreed. This level of customer service is pretty rare.

Its fine.  Go shoot it.

I might actually be impressed if they included it with each handguard like most others do, even those who sell their handguards for less than a third of G.

I would hope that they would reach out to him to fix it. Sounds like they sold him a shitty, used wrench. I've heard some pretty sad stories about the 'G' brand over the past six months. There's no way that I'd pay for one of their overpriced products, but to each his own.

I highly doubt that the OP ever got anywhere near 80lbs of torque, so 1) It shouldn't have broken like that, and 2) I doubt that you damaged the threads. If they're willing to send you a new tool and BN, then you might as well take it off and have a gander, though.


**Edit**
Just to add....I experienced a very similar event, which was wholly due to my own impatience.  Stern Defense handguard & barrel nut. I forgot to order their proprietary BN tool, and tried torqueing with a Brownell's AT  attached to my torque wrench.....which nearly rounded the SD BN

Stern Defense took pity on me, and threw in a free BN when I ordered their proprietary BN tool. Like the OP, I probably didn't need to remove and start anew, but with all new parts....why not? It's definitely worth it for the piece of mind.

Also.....strap-style oil filter wrenches are your friend!!

Cheers!

That is not needed.  Its fine.  Assemble and test.

theres a reason brand name tools cost more because they are BETTER quality. u get what u pay for........... snap-on , mac , proto , matco. fwiw and fror sure click typa...jmo

The tool in the OP’s picture sure looks like Geissele’s tool.  So it may have been an issue of the tool failing (it can happen even with high end tools), or the OP not quite using it right, or something else.

In any case, Bill’s stepping in and making it right was neither “expected” nor surprising.  Good firms come from good people doing their best to do everything they can to support their customers.