Greasegunner Posted October 28, 2021 Report Share Posted October 28, 2021 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 Thanks Haris Quote Link to comment Share on other sites More sharing options...
SGT Fish Posted October 28, 2021 Report Share Posted October 28, 2021 I believe the sear trip(?) is mounted in the upper, not on the bolt. So I'm not sure you can install a SA upper without it being modified Quote Link to comment Share on other sites More sharing options...
Saddle Ridge Armory Posted October 28, 2021 Report Share Posted October 28, 2021 Same LPK and sear as M16. No mod on bolt. The smith made a Slight mod on the upper to allow the sear to move. Small cut I believe. If you need pics PM me. Quote Link to comment Share on other sites More sharing options...
SGT Fish Posted October 28, 2021 Report Share Posted October 28, 2021 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 Quote Link to comment Share on other sites More sharing options...
SFG2017 Posted October 29, 2021 Report Share Posted October 29, 2021 (edited) 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 October 29, 2021 by SFG2017 Quote Link to comment Share on other sites More sharing options...
Greasegunner Posted November 1, 2021 Author Report Share Posted November 1, 2021 Quote Link to comment Share on other sites More sharing options...
Greasegunner Posted November 1, 2021 Author Report Share Posted November 1, 2021 The two bolt/bolt carriers are noticeably different and the receiver is even recessed for the little tab thats on the FA carrier. Does anyone know why they are different?? Quote Link to comment Share on other sites More sharing options...
SFG2017 Posted November 1, 2021 Report Share Posted November 1, 2021 I'm guessing the semi you have is a Gen1. My Gen 2 carrier is formed like the FA carrier but milled out like the semi auto. Purely a guess but I would assume the wanted to make the FA carrier heavier so it would slow down the cycle rate. Quote Link to comment Share on other sites More sharing options...
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