There is no extra charge from UPS for small arms ammo. A couple weeks ago I sent 2 boxes of 32Rem ammo about 100mi.
Box was 6"x6"x4" and weighed under 3lbs. Cost $28. UPS is
actually putting a sir charge on small packages through the back
door. They look at each package as a stop. They don't want the
small package trade from the public. If it was legal to ship ammo
in the mail same items would have fit small FRB and shipped for
$7.95. So you are much better off to sell locally or at a show.