I just received 6k 9mm casings by way of usps. Took two large flat rate mailers.
Boxes resembled those pictured previously. Back when I drove that fedex ground truck, I'd see boxes that were mutilated ... that shouldn't have been. And boxes that shoulda been trashed, that weren't. Any heavy object that isn't securely held inside the box, will obliterate cardboard. I also got to see the ratarded packaging that folks thought was sufficient.
Reflecting on it. 2x$14.95 ... $29.90. Fedex/UPS would likely beat that cost. The major carriers are more likely to appropriately handle items. Random rambling.