Geissele has made a trigger for the Sig Sauer MCX. In their Facebook post they claim that an MPX trigger is coming soon. That will be most interesting to see. For those who do not follow MPX accessory development, after market triggers are a ticking time bomb in the MPX.
Here is an email someone got from Geissele earlier this year.
Thank you for contacting us. In regards to our stance on our triggers in the MPX and MCX, as the industry grows, there are more and more AR variants out there that accept AR15 fire control groups. Each one is different and though we would like to, we have not tested our AR15 triggers with any of them. What we know about our triggers in the MPX we have learned from feedback from our customers. From the beginning, our customer service representatives have explicitly told people that we have not had any experience with our trigger in the MPX/MCX. We have stated that forum users have claimed to have success but we cannot confirm their success. We have never strayed from this and have never confirmed our trigger work in those platforms, and have always maintained that our triggers were designed to function with a mil-spec M4 carbine. With that said, the MPX has a very fast action, which is why the MPX ships with the trigger bridge, to protect the fire control group from the action. The MPX was designed to be used with the trigger bridge, our triggers were designed to be used with AR15 rifles using mil-spec components. While the MPX combination will work for a while, it will eventually fail. We want to be clear with our customers on this, and also have them know that we are working on an MPX specific trigger. We do not recommend using our AR15 triggers in these variants as it will void our warranty.
Going forward, rebuild kits for our AR15 triggers installed in the MPX will be available for a fee. The SSA-MPX trigger group is currently in development and will incorporate a trigger bridge to alleviate the current issues. It is slated for release in 2017. Unfortunately the SSA-MPX trigger is still in development and the price has yet to be determined as well as a definitive release date. Right now, we are not offering a trade in program.
As for the recent MCX recall, we have just recently heard of this recall and we are still working out all of the details. Right now, we cannot confirm this information. Once we get more information about this issue, we will let everyone know. I hope this helps.
From what I have heard, after market hammers have a tendency to break. AS the email above noted, the SIG MPX trigger has a hammer bridge. As seen in the rendering below.
Some companies have claimed that their triggers work in the MPX. Franklin Armory is one of those companies and I have personally been running a BFSIII Trigger in my Gen 1 MPX. I know quite a few USPSA competitors are running Hiperfire triggers in their MPXs as well but do not know the longevity of them in the MPX.
We shall see what Geissele comes up with. Hopefully we will see them again at the Big 3 East Media Event this October.