USPS registered mail is the only way to go, as mentioned above it's signed for every step and if it goes missing they know where.
Also, since Registered Mail is so well documented the insurance fee is lower than regular mail or UPS, usually enough that it's cheaper to go Registered than UPS.
And you should really take the time to read the
UPS Tariff/Terms and conditons of Service.
How do statements like
"In the event of loss of or damage to any part of property (including any part of a machine) which, when complete for sale or use, consists of several parts, UPS shall be liable only for the value of the part lost or damaged, not to exceed the declared value of the part lost or damaged. In no event shall UPS be liable for the value of the complete item."
figure into damaged barrel sets?
What about
"UPS shall not be liable or responsible for:
a. loss or damage to articles of unusual value (as defined in the UPS Tariff/Terms and Conditions of Service)"?
"F. Definition of Articles of Unusual Value Which Are Not Accepted By UPS For
Transportation
1. Shippers are prohibited from shipping articles of unusual value via UPS.
Articles of unusual value shall be deemed to include, but are not limited to:
a. Any package with an actual value of more than $50,000;
b. Coins, cash, currency, bonds, postage stamps, negotiable instruments
(such as drafts, bills of exchange, or promissory notes, but excluding
checks), and money orders;
c. Unset precious stones, and industrial diamonds;
d. Any article that contains more than 50 percent by weight of gold or
platinum, or any combination thereof in raw form, including, but not
limited to, bullion, bars or scraps of these metals.
2. UPS will not be liable for any loss of or damage to articles of unusual value.
UPS reserves the right, but is not required, to return to the shipper any package containing an article of unusual value. Such return will be made solely at the shipper’s risk and expense. I can see a claim for a $10K, 100 year old gun being denied because it of "Unusual Value".