I disagree Matt… the most accurate revolver I have is an 1859 Ruger Old Army, cap and ball (round lead ball) black powder … it is a .451 round ball in a rifled barrel… at 25 meters, it has a tighter group than my G34 … so I would argue (and can prove) that rifling does work quite effectively on round projectiles… Others have shot at black powder comps, with round ball and smooth barrels… they have about the same accuracy (or lack of) as our toy blasters.
A gel ball, however… is too easily distorted so will likely be compressed in the barrel, so it may have a flat front and concave back (in the barrel being pushed by the air behind it) … and once it leaves the muzzle, it probably springs back to being round, causing aerodynamic irregularities.
That is why, I believe, there is a number of FPS that is most accurate in a gel blaster…which from reading about others, as well as my blasters, it seems that 280 - 300 fps is probably the most accurate… I have also read that people chasing 400 FPS and above, have the punch, but seem to get less and less accurate as the FPS increases.
My guess would be that around 280 FPS, the gel stays round in the barrel. Also, gel balls are not regular enough in size, so some fit the barrel better than others, and the gels are also very slippery… so any rifling with ridges high enough to spin the gel on its axis, would have to be so long, the rifling would slice the gel open, as Daegis said.
Gel blaster balls are also very light weight, so they are easily influenced by drag and wind… plus, you can not always guarantee that only one gel ball is allowed into the T piece at a time… sometimes 2 try to load and the 2nd one gets chopped in half, impeding the next loading cycle… and bits of gels spitting out of the muzzle, sometimes accompanied by a full gel ball, other times just the bits…
These are toys, after all