Change the 308 recoil spring to something lighter? I bought a FM9 pistol and it drives me nuts with how hard it is to charge the gun. I was looking to see what others have done with theirs.

FM has some "interesting" marketing.  They recommend a 308 recoil spring to "help with feeding", then tell everyone that they need to use their proprietary length "slightly shorter than everyone else's extended-length buffer" to prevent trigger reset issues (likely caused by the 308 spring moving the bolt carrier too quickly).

You should be able to install a standard carbine spring and, if the gun is engineered properly, it will feed fine.  If not, the barrel can be sent to Rudy @ Macon Armory and for a nominal fee he can recut the feed cone so it will feed practically anything with a standard spring, like they all should.

Yep, FM operates like pharma.  Create the cure and then invent the disease.

This weekend I finally changed to a standard buffer spring and a heavy buffer. Worked great through 100 rounds with no issues. Charging it is a lot easier too.