Just spitballing…
Edited to provide moderator name and related thread: @Zee posted her hiking setup, which IIRC was a G30 mounted to her shoulder strap (open carry).
Depending on how small you plan on making your day hike backpack, you could also try a sling pack. I used to carry a sling pack on the motorcycle because I could rotate it around my body quickly and get to what’s inside (helped for toll change or a quick sip from a water bottle when stopped). Some sling packs have an extra “quick access” compartment seperate from the main compartment which might be good for your CCW. Personally, I used the slingpacks with a chest strap to stabilize it while leaning off the bike in turns (might be helpful with active hikes).
I’ll add, that I use small sling packs, as the bigger and heavier they are, the less handy they are to rotate around. It might not work well if you have bulky or heavy gear.