I tried shooting miniature darts, not as weapons, but for a laugh and into a dart board. I thought I could achieve better accuracy than throwing it by hand. I was wrong. The darts heads were too light for the fins. I scaled up to bigger darts, but the flights would fly off because the velocity was too high. I glued them in, but the transition from vertical in the pouch to level flight was hazardous and unpredictable. I never tried horizontal launch like a crossbow. That would be too weapon-like for my fun-inspired purposes. That's the way to go though, IMO. Unless you can guide it in a channel, I would fire it with the traction leading from the tip, rather than pushing from the tail. A sabot may work.
One of the few designs that worked well was the finned football you see below. It and its brothers were shot nose down in the pouch (foolishly from a regular hand catty) and always hit nose on. I didn't do any serious bench testing of accuracy or velocity. I was working towards the next stop being expanding or frangible shot that would dump energy and not penetrate or rebound. Like the Glaser Safety Slug this was intended as a safety feature. Most of these mechanisms depend on deforming in a predictable was with one end hitting first, so I needed fins. I was unable to determine whether making expanding ammo would be illegal, so I stopped there.
If you are to make fins, they need to be small enough not to reduce velocity. The way reduce drag and not lose too much control authority is to put a tail on. That's why darts and aeroplanes and helicopters have tails. Darts with long tails won't last more than one shot, obviously.
I guess the reason you want to do this project is spin stabilisation. For that you don't need a tail. There's really little point doing it to reduce cross sectional area. There are easier ways to reduce drag. The only other reason one might want to add a fin might to be make penetrators. Unless you're shooting at flak jackets that's not necessary as for hunting, you really want to dump energy and stun or kill the prey rather than stabbing it. If you are doing it for penetrating body armour, I'd rather not know about it.
