A Super-Soaker 5000 filled with Lysergic Acid Diethylamide.
So... your ammo would cost thousands upon thousands of dollars, and in a few hours might make them hallucinate (if it gets absorbed through the skin)? May as well fill it up with bleach or something cheap lol.
Same with the US really. It's a massive and thriving industry, but there is plenty of anti-gun sentiment flooding the country. I know all about that story, don't need to tell it to me. I read about it a long time ago, scary the way the government wants us all to be so weak and helpless.
In this day and age the army is far past anything a citizen group could do, even with state of the art guns. Gun control has its merits, especially for small arms. If we did have another civil war, what use would a scrappy group be against a well trained military with tonnes of weapons and equipment?