Messing around with Alexander Blade Scripthook I've made some edits in the sample NativeTrainer.

UPDATE:

NEW VERSION - STORM GUN

Install the same way as shown below, but now to use activate WEAPONS > STORM GUN

After the option is activated the lightning will strike where the bullet hits.

NOTE: change the weather to the overcast/storm so the lightning start working quicker, as the first few shots will "call the storm", when it arrives most of hits generate lightning bolt

Previous version:

To use the mod:

1) Install the most recent version of Alexander Blade Scripthook 
(http://www.dev-c.com/rdr2/scripthookrdr2/)

2) Extract my NativeTrainer.asi  version into the game directory (where RDR2.exe and Alexander Blade Scripthook are located)

3) Use F5 ingame to activate the trainer menu.

4) Enter WEAPON menu and enable POWERFUL GUNS

5) Hit F1 to strike a lightning 15 meters in front of you

All credits go to Alexander Blade