I’ve been using a backpack as a range bag for a while now, and I don’t know why I ever used a conventional gym-bag type range bag for so long.
It certainly depends on what kind of shooting you’re doing—if you’re a skeet or clays shooter and your bag will regularly be toting five or more boxes of 12 gauge field loads, then you probably want to stick with the overbuilt, dedicated range bags that can handle that kind of weight.
But for rifles and pistols at the range, I realized I’ve been hauling my ammo in a large ammo box instead of a bag anyway. Mostly this is to ensure I'm in compliance with my local laws, but also, its easier to keep everything neat and organized, and to make sure I'm not forgetting anything. Plus it's a lot easier to dump collected brass in an empty ammo can that can be rinsed out later, but I digress.
I recently got my hands on a Stingray pack from Blackhawk! and it’s a perfect choice for a "range pack," if that can now be a thing. It's a great choice for an all-around backpack too.
First of all, the pack (which comes in two sizes) opens up all the way, and I mean all the way, allowing you to lay it down flat and get to everything all at once, like a duffel bag. Alternately, the main enclosure has four zippers, which means you can open it up a little bit from the bottom or the top, left or right side, so you can get to anything you need without fully flopping the pack open.