I have the Colossus - fits full-size P220 in the back panel. This shoulder pack is unbelievably well made. I managed to fill it with more weight than I could comfortably carry (on one shoulder). I use the simple Max holster - attaches to the velcro panel in the pack. Holds 3 mags in the front compartment.
A double stack semi-auto may be too wide, others may not have an issue. I also switch out to a Ruger LCR with 3 loaders.
I have more than a couple of their packs - my Falcon II backpack carrys LOTS of stuff and is easy to hike with.
I wish there was a local store that carried the Max line so I could touch and feel.
Check out
www.edcforums.com for lots of info about Max & other brands.