Got to shoot an original Remington 10-bore Howdah pistol an the Vintage World Cup last year...it was pure whoop-de-do! We ran out of brass-cased 10-bore cartridges and started going through 10 gauge shotgun shells. That, by gosh, is the perfect "car gun!"
I've always wanted an Ithaca Auto & Burglar sXs 20-gauge pistol, ever since I handled my first one at the old Tupelo, MS, "Gun Show" back in the 1950s — acres of guns being sold out of the back of car trunks, folding tables, etc. In its absence, I do like the Bond Arms .410 derringer...pain is your only friend!
Michael B