Floating flak projectiles is FPSC bug. Usually if you don't restart FPSC after adding a new weapon you will have errors of some kind. Flak sometimes requires rebooting the PC to fix.
Quote: "also the rpg is supposed to stay on-screen when it runs out of ammo but for me, it disappears!"
It disappears for everyone. That's the way FPSC handles weapon-is ammo weapons like the LAW or grenades. Your choices are basically to have it disappear or stay on the screen and still see a rocket loaded. I think disappearing is the lesser of two annoyances.
Quote: "and there isn't supposed to be a crosshair. There isn't one located in the weapon directory but the software automatically makes a tiny white dot for a cross hair. is something wrong with my download?"
For whatever reason, I must have forgot to include the blank crosshair. This is the first time it's been brought to my attention, please use the attached "blank" crosshair to remove the dot (FSC default if no crosshair image found).
Quote: "Some mods also make problems with the RPG"
Which mods and what problems?
I'm aware most mods cause the flak projectiles to come out backwards. Thare two .x projectiles included in the flakspec folder for mon/non-mod which will hide that particular issue.