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MCX Failure to fire with new trigger

This is a discussion on MCX Failure to fire with new trigger within the SIG Sauer Rifles forums, part of the SIG Sauer Forum category; I recently picked up an MCX in 556 and, as with everyone else it seems, swapped the trigger almost immediately for something better. Inspecting the ...


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Old 07-26-2016, 08:22 AM   #1
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Join Date: Jul 2016
Location: Denver
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MCX Failure to fire with new trigger

I recently picked up an MCX in 556 and, as with everyone else it seems, swapped the trigger almost immediately for something better.

Inspecting the factory trigger I noticed that while the trigger sear was nicely polished, the sear face on the hammer had a large bur on the lip which caused the lumpy gritty feel to the factory trigger.

I didn't want to depart too far from the factory single stage trigger so I picked up a BCM nickel teflon trigger kit and the JPS4.0 "enhanced reliability" 4-4.5lb. springs from JP.

With the trigger and springs installed there is literally zero slack. I don't have a trigger pull gauge but I would guess it to be in the 5lb range before it breaks. Since it has no slack to take out, when you apply pressure to the trigger it remains rigid until it breaks cleanly. I have to say it took some getting used to a trigger that doesn't seem to have any pull to it prior to breaking.

Now to the issue I experienced. This occurred 3 times and was always on the first round of the magazine. The first round would be loaded, either using the bolt release or by manually racking it, and then when the trigger was pulled it would click but wouldn't fire. Ejecting the round showed zero signs of a strike from the firing pin, not even the slightest dimple.

Any ideas what would be occurring if the trigger is audibly releasing but not firing the round?

I'm thinking it's the bolt stopping short of locking up but figured I would add the trigger info just in case that might have something to do with it as well. I was shooting American Eagle brass cased 556, so no crappy steel case stuff.
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