Shipping small boxes I use the automated USPS system.
Asks you questions on a screen.
I'm never ever shipping anything illegal and never will.
But the automated system takes the interactive human decision out.
Paste on the self stick mailing label. Pay for your purchase with CC. And in the mail slot the box goes.
Only downfall is box size. Don't think a broken down muzzle loader would fit in the drop box.
So think about trying the 24 hr automated shipping/ mailing kiosk at your USE office.