I know Gen I MPX parts don’t work on Gen II (bolt and barrel at least don’t and magazines are a maybe) but I’ve recently heard about Gen III MPXs (don’t know if a 3rd Gen is official or just another rolling design update from Sig) had wondering if Gen II barrels and boots will work in the newest models?

My experience with MPX or lack thereof.

I ordered an SB Tactical collapsible brace to replace my copperhead’s rectangular pivoting brace which I dislike. I tried to install it to no avail. The metal rods are way thicker compared to the brace that came with the copperhead.

I couldn’t find any information about the “fitment” issue I’ve
encountered anywhere and decided to return it but as of this writing, I am still waiting for my RMA request. It’s been a week so far.

Did anyone else in this forum ran into the same fitment issue?

Regards.

There is no official Gen. 3 MPX. However, the upper receivers on some models uses a very different ejector and has no cam plate. This different upper can accept the Gen. 2 barrel and bolt. There are some minor differences between Gen. 2 bolts, but they are all compatible with the Gen. 2 barrels.

You can spot the newer upper receiver by lack of the external cam plate and the ejector is held with two external screws.

There are two different bolt carriages that require different recoil pads. One recoil pad in the lower is orange and is used in both Gen. 1 and 2 lowers. The second recoil pad is a black truncated cone and is only used in some Gen. 2s that have a carrier that has a rear that fits over the cone when it in in recoil.

Bill