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Sig Mpx Full Auto Conversions


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Hello All:

I may acquire a FA MPX that was converted from a semi auto

Does anyone know if there is anything done on the upper(the bolt) and what was done?

The lower looks like M16 trigger groups was installed as well as the sear.

I am wanting to swap the upper and I guess the bolt needs to go into whatever upper

I am swapping out

Any help would be appreciated





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I just double checked. The semi uppers do typically have the full auto sear bar, but have the mounting slot and holes for them. You can find them with a quick Google search. You'll need one for each upper that you want to use with with FA lower. They just mount in with a couple roll pins

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Trip bar for the upper is needed.  The lower uses a standard M16 auto sear that is tripped by the bar.  The tricky part is the action of the gun abuses the trigger group.  That is why they have a disconnector cover in them.  No one sells a full auto trigger group for the MPX.  I've reached out to Timney and Geissele about it.  Timney won't reply to inquires and Geissele said they have no plans to unless they have enough demand (they wouldn't clarify what enough is).  I've tried modifying triggers to fit and they all end up breaking.  I broke the factory disconnector cover from Timney and another I made in house out of aluminum to work with a POF drop in trigger, it broke immediately too.  I also bought a Geissele MPX semi auto trigger and used a Geissele FA hammer slightly modified to fit and it broke the hammer.  I've tried slowing down the action with Geissele springs with the Geissele trigger group and it kept jamming the gun until I used factory springs again.  I've spoke with other SOT's and they are getting the same results but just change the hammer out when it breaks.  The first two disconnector cover broke within 100rds and the Geissele hammer broke around 200rds.


Edited by SFG2017
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