I'm going to be working all summer in Inyo National Forest, Sequoia, and John Muir Wilderness with the Forest Service. This will entail going light on 5-9 day wilderness monitoring backpack trips. To the point: how much bigger is the 50L from the 47L?

Exos for sure. It behaves and packs like a regular internal frame pack, but weighs about the same as a frameless.

got it simon, Pretty funny that you fielded my ? man. So here's my deal: I usually use an 80L arc'teryx bora...i'll be using that on the 9 days guaranteed. just looking for something smaller/less bulky for the shorter strike mishes. so exos for the shorter ones you say? cheers bro

Andy, If you're considering backpacking with the Jam, know that 47L isn't going to make much difference from 50, both are likely going to be too small. More important would be that the pack fit you well, and for your torso size, I'd recommend the Medium. Beyond that, however, I'd recommend that you simply get a larger pack. For 5-9 day trips in the Sierra, since you'll be required to carry a bear canister, you'll have trouble fitting all of your food into a pack of this size, even with a tiny down bag, minimal clothing and an ultralight tarp. I think you'd be really happy with an Osprey Exos 58 Medium. Even though it is slightly heavier and more expensive, I think you'll find that the aluminum frame supports the load better than the flexible panel on the jam, making the pack carry better. Also, the exos fits both the Garcia (black) bear canister and the Bearvault (transparent blue) quite nicely in a convenient lateral orientation. Finally, I think you'll appreciate the multitude of organizational pockets on the Exos. Congrats on the job!