For skirmish level TSR Boot Hill wild west games I use the following fumble table:
Occurs when you roll very badly on your "To Hit" percentile dice.
Roll a 1d6
1. You lose your balance and stumble. Your weapon discharges and the bullet hits your foot resulting in 50% loss of movement rate and 1-3 points of damage.
2. Your weapon catches on your clothing and discharges, hitting one/any random person (including self) within 10 feet for 1-3 points of damage.
3. Dust, sand, debris, smoke, or powder gets in your eyes resulting in 50% loss of movement rate and the inability to shoot during the next turn only.
4. You stumble badly, and drop your weapon to keep from falling. You cannot use any weapon during the next turn but can move at normal movement rate.
5. You hit an unintended, random, person within a 20 foot radius of your target for 1-3 points of damage. If none are in range, you simply miss.
6. Your current weapon jams and cannot be used for the rest of the battle. You may switch to another weapon and begin shooting next turn.
At the end of the skirmish I use this table for those who were shot down during the gunfight:
Roll Him Over
and roll 1d10:
1. Player is alive with a scar. Authorities now have identifying marks for wanted posters.
2. Player is alive with a scar. Brawling and grappling is reduced by 10%.
3. Player is alive with a scar. Throwing accuracy is reduced by 10%
4. Player is alive with a scar and noticeably limps. Running and dodging is reduced by 10%.
5. Player is alive with a scar and gun/knife accuracy is reduced by 10%.
6. Player is alive with a scar and gun/knife speed is reduced by 10%.
7-10. Player is dead.
link
link