Mossberg 940JM pro charging handle failure

[u/Inevitable-Click-129]

Here’s a fun failure I’ve never seen before! Happened during clay match. To be fair though I love this gun and have shot thousands of rounds through it.

Thought I would share with the group. Has anyone else experienced something like this?

[u/Acceptable_Visit_115]

The broken cross-section is consistent with a high cycle (low stress), reverse-loading fatigue crack (see diagram below). I've seen failures like this across quite a few guns, most of them have a heavy "knob" style charging handle.

When the bolt slams to a stop at the two ends of its travel, the inertia of that heavy bolt knob will want to continue traveling forwards/backwards a bit. This causes a tiny bending moment on the shaft. After thousands of rounds metal fatigue takes its course.

[u/CrowsFeast73 → u/Acceptable_Visit_115]

Makes sense that the thread itself would eventually propagate as a crack.

If there's an aftermarket option with a smooth shaft then you shouldn't have this issue again.

[u/Acceptable_Visit_115 → u/CrowsFeast73]

Yup, threads in bending is almost always how these things happen.

Beretta's extended charging handle for example uses a locking mechanism with no fasteners, and the extended knob itself is lightweight plastic molded over the steel shaft to minimize inertia. Benelli M4 also uses a captive shaft.