i would say something like this....i am not up with my ufopaedia knowledge, so some interpretation may be required also i may have left some out (probably in fact).
mellee weapons.
knife: very low - med damage 4 TU.
pistol whip (pistol, machine pistol, micro shotgun, maybe smg): very low to low damage, very low knockout chance, low-med stun chance. 4-5 tu
alien knife: low to high damage 8 TU
2nd alien knife: med to very high dam 8TU.
rifle bash: low - med damage, low knockout chance, med - high stun chance. 10-12 TU (maybe 8 for shotgun)
stun rod: no to very low damage, high knockout chance, very high stun chance 8-12 tu.
advanced stun rod: same as stun rod, with maybe a 3-5 square range.
the rest of the weapons leave TU as is.
close combat weapons
pistol - low damage, can be fired in mellee, very accurate 0-3 squares, accurate 3-5 squares, inaccurate 5-10 squares, very inaccurate 10+ squares.
machine pistol- as above but take off one square for each accuracy range.
flamethrower- max range, 6 squares, med chance of fear. high - very damage can be fired in mellee.
micro shotgun - melee fireing, same range as pistol or machine pistol, higher damage.
shotgun - cannot be used in mellee (must us bash, but at cheaper cost), range 0-5 very high accuracy, 5-10 high accuracy, 10 -12 med accuracy, 12 - 15 low accuracy, 15+ very low accuracy.
assault weapons.
all assault: no melle range, 0-10 very accurate, 10-15 accurate, 15-20 med accuracy, 20 + low accuracy.
heavy machine gun - same but slightly less accuracy.
grenades
flashbang - high stun chance.
shockwave grenade (researchable) -high stun chance, med knockout chance.
normal grenades should maybe have a slight stun chance as well.
and incendary should have a slight fear chance.
other weapons
grenade launchers and rocket launchers should have about the same accuracy as assault guns, with limited to no bashing ability.
sniper rifle should be able to be bashable and should have the most accuracy out of any weapon.