I submit the following rule for your enjoyment, or not, depending upon the outcome to your gun battle(s).
When reloading, each side selects a D6 die, and secretly chooses how many shots they want to reload, before firing again, e.g. 1 – 6, by placing the die under their cupped hand, and uncovering it at the same time as his opponent (upward facing surface is the number of rounds you wish to reload).
For NPC's, you can just roll a D6 randomly in order to determine how many rounds they want to attempt to load, before firing.
They then roll a separate D6 die, and add the result to the number of shots selected for reloading.
Low die wins initiative (gets to fire first), and the difference between the two rolls is the number of shots the initiative winner gets to fire at his unmoving opponent, who if he is smart, will be crouching down to present a smaller target.
If players wish to move while reloading, they can do so at a walk, but only reload half as quickly, while still suffering the full penalty for reloading, e.g. can reload 1 bullet on a 2, 2 bullets on a 4, and 3 bullets on a 6 (on a D6). Only even numbers count, in terms of initiative, while moving, since the reload time is slowed while moving.
Note, this may permit the reloading character to gain some cover, e.g. behind a barrel, or water trough; getting to the corner of a building; getting inside a building, etc.
Firing takes place, as normal. Ties are just that, and permit each gunfighter to fire at the same time.
Example, Black Burt and Willy the Kid are in a gunfight, but since both have been drinking heavily, neither is shooting up to snuff.
Both have fired at each other, emptying their guns, but all of their bullets have missed.
They then attempt to reload.
Black Burt, being a heavy drinker in the past, is less affected than the Kid judgment-wise, by the alcohol. He decides to reload just two bullets in his gun, in order to try to get off the first shot.
The Kid, on the otherhand, decides to fully reload his gun with six shots, since his aim has been so poor, he wants to have a full load of ammo for the next round. He crouches down, while reloading, to present a smaller target to his opponent, since no cover is within reach at walking speed.
Burt selects 2 bullets, for a 2, and rolls a 3 on the D6, for a result of 5 = 2 bullets, plus 3 for the random die roll (2 + 3 = 5).
The Kid, being younger, and despite his drunk condition reloads quickly, with the following result 6 bullets, plus a one for the random die roll = 7 (6 + 1).
Comparing the two results, Burt has a 5, so gets for fire first, and the Kid has a 7; therefore Burt gets to fire 2 shots at the Kid, before he can return fire (5 and 6 is lower than 7).
If Burt had chosen to reload three bullets, he would still get to fire first (result of 6), for the first round/bullet, and then additional shots would be simultaneous with the Kid's firing, e.g. 6 is lower than 7 for the first shot; and 6 + 1 (for the second bullet = 7) which ties with the Kid's first shot.
Burt's chances to hit Willy still aren't good, due to his drunken condition, and the fact that the Kid is crouching down. He normally would hit on a 9+ at this range, in his condition, but Willy gets a +1 modifier to the die roll for crouching, thus becoming a smaller target (Burt needs a 10+ on 2D6 to hit).
Burt rolls a 7 on his first shot, using 2D6, missing Willy.
On his second unopposed shot, he rolls a 12 on the 2D6, finally hitting Willy, as he continues to reload his revolver.
I'll leave it to you to determine the outcome, using your own rules.
It sounds complicated to explain, but in practice should be relatively simple, once you do it a couple of times.
Enjoy!
Best regards,
Rob