Are you dry-firing without a magazine in the gun?
If the magazine is out, the trigger is disconnected from, and is not moving, the striker. When the magazine is in place, the trigger is moving the striker back against significant spring pressure.

See pp. 10, 11, and 23, after clicking on: FMK Firearms Model 9C1 Catalog

The long, hard trigger pull is a major safety device, in this gun.
The only way to overcome the difficulty you're having with the trigger pull is to exercise your trigger finger, and improve its strength.
There are several devices which will help you to do this. The important issues are twofold: First, you need to exercise the trigger finger. Second, you need to be able to isolate your trigger-finger's pull, to keep it from affecting the grip of your other fingers on the gun's handle.
The device that my wife, Jean, finds most useful for doing this is the Gripmaster, in its Medium version (click on: http://www.prohands.net/products/gripmaster.php). She grips the device with her lower three fingers as if it were a pistol, and then, maintaining that strong grip, she separately presses the index-finger pad of the device.

Originally Posted by dtvonly

I have an FMK 9C1 DAO gun. Dry-firing has a very light (but still long) trigger. With a snap-cap, the trigger is still light (and long). However, with a real 9mm round, the trigger got much heavier to the point that it seems not to want to release the firing pin. I really have to pull very hard. Why the differences among the three types of trigger scenarios, and how can I lighten the trigger with a real 9mm round? Thank you.

dtvonly, how happy are you so far with this gun? I have never seen any around where I live, but have read a couple of articles on the FMK.

Hi berettatoter. I chose the FMK for price, slick design and feel. Other than that I do not like long and hard DAO trigger. I don't know where you are currently residing. FMK main headquarter is in Placentia, CA. I am only about 25 minutes away.