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Posted (edited)

How come some bolts have this ramp in the front part of the gas key dummy (not sure if that's the correct term for it, but dummy felt right...)

My Foxtrot Mike bolt has a ramp like that, and when I pull the charging handle it pushes the bolt down slightly because of it.

So if I pull the charging handle while there is no mag inserted, the bolt will drag slightly because of it.

But when there's a mag with bullets inserted, it will push up on the bolt and counteract this.

So it really isn't a big deal, it's just slightly annoying. 


I'm just curious why they would design it like that?

It's not just FM. CMMG and even JP has bolts with this design.


Some seems to have a design without the ramp, like the one in the pic from Angstad arms, and Taccom.

That seems like a better design to me. But for some reason they then place it further back on the bolt...

Is there a shorter charging handle you can use for these?

Or should you just accept that there is some slack in the charging handle before the bolt starts moving...?


Am I missing something?






Edited by grottulf
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The charging handle on the Angstadt Arms and Taccom type bolts engages the step in the front of the bolt, not the dummy "gas key". At least in my two side charging uppers (older Matrix Arms and NFA) with Taccom bolts, that's how the bolt is engaged by the charging handle. The dummy "gas key" is just there to keep the bolt oriented correctly. And the Taccom bolt key is much lower than any others, it completely dispenses with the taller portion, and is just a figure "8" shaped thing around the two bolts holding it on.


Why other bolts have a sloped face on the key, I cannot answer that. Maybe they want the charging handle to exert downward force to aid in cocking the hammer? That's just a guess, and probably wrong.

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Crystal clear! 👍

Thanks for the clarifications, guys!

It's strange that FM made the ledge so small.

It's only about 1mm (0.04") on my bolt.

The angled part could be much smaller and still clear the radius of the charging handle.


And I suspect the tolerances between the upper and the bolt are a bit loose, because the charging handle slips of the ledge and pulls on the angled section instead, when the guns not loaded.


I hope that has been fixed in their revised bolt, that they have promised to send me.

I just have to wait until Brownells starts to export gun parts again, before they can ship it to me.

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