Looking for some help. I had a spare grip and a a spare full size slide laying around. So I found an X5 FCU. Supposedly you can drop an X5 FCU into any grip and it is supposed to work. So says Sig when I called them. The X5 FCU will install in the grip module with no issues but when you install the full-size upper, the trigger will not engage or fire the weapon. Have not loaded any ammo into the gun yet. Have only attempted several dry fire. It seems there is some sort of disconnect. Here are some pics. #1 and 2 are standard P320 FCU with only a X5 trigger installed. #3 is the X5 FCU. You can see the differences that I circled. Any help would be appreciated.

https://i.ibb.co/ZLqcDtP/A9448...6-CE6073-D71-DCF.jpg
https://i.ibb.co/fxX58ZT/F8-A4...-9-D5461-B06-C05.jpg
https://i.ibb.co/ScT13HN/4-F0-...-134-A3-BF4-A521.jpg
https://i.ibb.co/c3b9GnG/A1705...-8-A02-FA67916-A.jpg
https://i.ibb.co/5hVhk14/B7086...DF-883946-BCADC7.jpg

The FCU you have labeled as #3 has had the safety upgrade, it appears the others have not.

If the slide has not had the safety upgrade done, it will not work with FCU #3. The updated slide has a groove milled out to accommodate the pawl you see on FCU #3.

Thank you 10-7. That is the info I needed. All my slides are pre-upgrade and I had nothing to compare to. I prefer my P320 pre upgrade. Have not sent mine in. Going to have to find another one or sell it.