Cross-posted from AR-15 >> Build It Yourself
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 too long to hit 40 lbs, then it busted. The torque wrench definitely never clicked. The barrel nut wrench was used before I acquired it - not sure how much, though.
https://imgur.com/wVIjXikThis pic shows how close the barrel nut is to the receiver. Would this normally sit flush if it was properly torqued or over-torqued?
https://imgur.com/ZPma5iuThe slot for the barrel nut wrench nub doesn't seem deformed, just a little marred up.
https://imgur.com/kOVhNOIThe barrel nut wrench.
The feed ramps and barrel extension are aligned perfectly, which tells me that the index pin slot is not deformed.
I was concerned that I over-torqued the nut and potentially damaged the threads / receiver. Several members in the Build It Yourself forum stated that it is very unlikely that the nut was dangerously over-torqued and that the upper is fine as it is. I wanted to check in on this forum to see if there was any further input or recommendation on leaving as is / removing barrel nut and torqueing to correct ft lbs.
Thank you for your time.