You are correct about the power of .410 shot in a handgun.
The powder needs confinement and pressure to burn properly and produce more pressure to provide velocity and energy to the pellets. Think of it like trying to make a pea-shooter out of 1/2 inch pipe. You just cannot get enough pressure built up to do anything.
The down-side is no penetration. The up-side is no kick.
If you need snake medicine, they used to have shot shells for your ACP. If you need crook medicine and don't want solids, there are always Glaser safety slugs.
I'm poor, 'cause I can't stop playing with guns.
MRS