Where can I send 16 gauge handloads to be pressure tested?

Just a FYI, I believe Armbrust is the only one who will test factory loads.

This is the last contact infro I have for Tom Armbrust, but I would call first - 815-451-6649
1108 W. May Ave, McHenry, IL 60051

https://www.precisionreloading.com/view.php?pg=shot_proof

Scroll down to the bottom on the left "Ballistic Testing"
http://www.downrangemfg.com/index.php?option=com_content&view=article&id=54&Itemid=62

You can't use the USPS for live loads

As Drew mentioned, live ammo can't be shipped by USPS. I shipped rounds for pressure testing yesterday at UPS. It is a 20 minute drive from home to the UPS Consumer Counter at the UPS warehouse. Be prepared to pay through the nose as an adult signature is required which runs up cost. UPS Stores are franchises that won't ship ammo. There was a counter sign dated Aug 2022 that stated" guns or gun parts can no longer shipped by UPS except by "return service". The clerk said that UPS requires an FFL to ship. She speculated that it would be a matter of time before ammo shipments were prohibited--pure speculation on her part but who here would be surprised? As Brent mentioned in another thread, length of chamber in testing gun is critical in establishing short shell pressures. Boyle's Law regarding gas pressure and volume is at play rendering inaccurate shell pressures for shorter than 3" ammo in a 3" pressure testing gun chamber. For shortshell (2") 12 gauge, Tom Armbrust refers such testing to Bruce Ducksworth, Bruce's Big Bore Ballistics,
130 Ben Anderson St, Mount Vernon, Ga 30445
Email 338lapuaba@gmail.com
912-423-0334

You need a firearns shipping account to avoid all that.