I've had two Fireballs, and I've found it to be a useful little cartridge.
First rifle was a Sako 461, and the Fireball was perfect match for this small action. Sold it in a fit of silliness. The second rifle was a Rem LVSF, and the round just didn't work for me in this action. I had all sorts of feed issues, and eventually gave up and had the rifle rechambered to a 222 Rem Mag.
I don't have access to Lil Gun, but it was simple enough to come up with loads using ADI (Hodgdens equiv) powders that pushed a 40 gr bullet at 3400 fps. Using small loads of fast powders, it was also easy to work up loads that made very little noise, and emulated a 22mag.
I only used Vmax bullets, and they aren't fur friendly in anything. Using a 50 gr bullet at about 2800 fps might give you what you're after.
