Mike,
The idea of installing & using a "toothy" breacher choke as a pain compliance device on a shotgun is ill-advised.
You don't want to get that close unless you have no choice, distance is your friend.
If you do find yourself forced into contact proximity, you do not want to be jabbing somebody in the chest or stomach with the end of a shotgun to persuade them to stop whatever it is that they're doing, or getting ready to do, to you.
You get that close, you're essentially handing them your gun. A grab reaction is almost inevitable, at which point you find yourself wrestling for possession.
Unless you're bigger, stronger, more pumped, or you've had some instruction on baton/long gun retention and recovery, you're quite likely to lose.
If the situation indicates you having a shotgun in hand, it's use is as a firearm, not as a club or pain compliance device.
You run the additional risk of not only losing the gun, but having it either fire accidentally during the scuffle or having it turned on you.
One of the last things you ever want to do is put (or get) yourself into the position of wrestling with someone over a gun, of any type.
Yes, a chest rake can work, but when would you use it? Unless you're in law enforcement & required to physically engage and subdue a subject in terminating the encounter, there's little other reason to do so, and for most situations the risks mentioned don't justify it.
Denis