That may seem logical but it's not true. Even if the pack frame is that open upside down U shape with absolutely no other members, the forces aren't going to be acutely focused the way they are when you're making a bend in a tube using a lot of mechanical advantage.

Now attach the legs of the U together and it becomes much stronger. Constrain the frame with taught fabric, or diagonal stays (could be thin cord), and it becomes stronger still.

If you throw the pack off a cliff and one of the frame members lands on a rock with the weight of the pack on it, sure, you might wreck the frame. But just day to day use? No way.

whether it's a big difference or not, it may still be plenty for the application in the tubing sizes that are practical to use

and it's unlikely you're going to heat treat to T6 at home, the process is not trivial

anyway my point isn't that you should use specifically 3003, but that materials should be chosen based on their strengths. this application does not play to 6061's strengths, it's just an alloy people know about. so use something that is either formable cold, or that won't be negatively affected by local heating

and either way you should be using a tubing bender that supports the walls of the tubing to prevent kinking and flattening, if you're trying to push the limits of the material. the most important thing here is keeping the tubing tube shaped through the bend

6061 isn't nice for bending in general, 3003 is a lot easier to work with and I doubt the strength difference would matter

Dan with the frame from his Kakwa 40 pack.

Apparently it’s pretty challenging as a DIYer to bend 6061 tubing without creasing it or causing wrinkles, and requires you to fill the tube with sand before forming.

knew a girl in high school who wore crocs a lot

Is that Houshou Marine?

There's sick fuckers who literally fap to women's haircut videos and stylebooks.

imagine Cain and Abel as cute anime girls UwU