When you have an attached grenade launcher on your rifle, you grip it by the barrel of the grenade launcher.

If you cycle to the grenade launcher by using "F", the soldier should move his hand to the grip of the grenade launcher. Then when you shoot the grenade launcher, the soldier should pull the trigger on the launcher. If you then cycle back to your weapon by using "F", your hand should move back to the barrel of the launcher.

Currently, when you are using the grenade launcher, your hand stays on the barrel of it. And when you fire it, you're pulling the trigger to the gun, which shouldn't be possible unless the grenade launcher was attached to the gun, and you were able to have a selective fire that switches to the grenade launcher. And I'm quite sure even the gun in this game isn't capable of that. {F18853}