Not sure if this issue belongs here or the reloading forum, but here it goes. My MPX has been having some FTE issues with my reloads. Ran 5 mags of factory 115 with no hiccups. Rounds run fine in my pistol and in other 9mm carbines. 1.130 OAL with Everglades 115 Plated. Don’t understand why it won’t extract the reloads. Cases don’t appear to be bulging and like I said they shoot fine in other guns. Any thoughts?

Should probably change the title.

There’s no issue with the rifle. There’s an issue with your reloads.

As above; my guess would be that the reloads are simply outside the MPX’s designed operating envelope. The powder and charge weight you were using is important as it may be a fast powder, as many popular pistol reloading powders are, that minimizes charge weight and felt recoil to appeal to target and competition shooters. It may just not generate the necessary gas volume to fully cycle the MPX.

The fact that they functioned in other pistols is not necessarily an indicator, unless those pistols were also gas operated.

The reloads could be too low powered to have enough bolt velocity to eject them or they may fit too tightly in the chamber. My subsonic reloads sometimes don't lock the bolt back on the last round because they are low powered. You can check the chamber fit of your reloads by removing the upper and bolt carrier assembly and dropping them into the chamber.

Appreciate the replies. I thinking I had a few pieces of brass that were reloaded a few times too many and were swelling in the chamber.  Made a batch with fresh brass and same bullet/powder grains with no issues.