Nothing good existed I could find, so made one. Have a not very hard to get to, but hidden little steel rack in the closet, carbine rests vertically in it. Padlock for the blind (pushbutton, can do without looking, but no electricity!) keeps the gun in place and blocks the trigger so it can be left loaded.
Not milliseconds, but can get it in action in say 10 seconds making noise, 20 if quiet.
More options since. For rifles still because why get in a gunfight with a handgun if you don't have to, I like these:
https://www.deansafe.com/products/vli-51653-sa
Designed to be stuck in a hole in the wall, between studs, but no reason you couldn't just mount it TO the wall instead if you didn't care.
Note the Simplex (or knockoff?) lock, so again pushbutton but no batteries. Click around, they make smaller ones if that's too much disruption.
Also consider the second layer, especially if you go with a somewhat cheaper one, a remote alarm. We use Wyze cameras, and their door open alarm is cheap, can make your phone beep when not in the room or even at home, to say the safe is open. Then you can act appropriately instead of being surprised later.