Bond Arms Backup (45ACP)
This is the only Derringer style addition to this list, but it’s a new and noteworthy pistol with a lot to like for the shirt pocket crowd. Firstly, it’s available in a variety of larger, readily available calibers like the 45ACP.
As you can see, it’s a two-round capacity pistol, designed as your “Backup” when the chips are down… or something. With a overall length of 4.5 inches, it’s pretty compatible with shirt pockets and self-defense. It’ll also turn heads and get lots of attention at the range. It does have a safety.
On the heavy side (18.5 oz unloaded) it may be less-than comfortable in your shirt pocket, but it depends on how much its wild-west style is worth to you.