I received an interesting email from Steve @ Matrix...as follows.
"I received the ruling from the US Customs yesterday and they have made a ruling that my bullets are "ammunition" and therefore require a permit for each customer. When I started this company a number of years ago I received a ruling that bullets were exempt because they did not include a propellant or primer and, therefore, could not be considered a cartridge or ammunition. Sometime in the last few years this definition was changed and all sub-components were included. I suspect this happened last Dec because Canada changed a lot our import rules.
Unfortunately, this ruling prevents me from shipping anymore products into the US for the near foreseeable future and ultimately probably will shutdown the business."
So, if you're like me...you'll have to apply for a permit to order from him or move on to the next thing they ban.
. "Application and permit for Importation of Firearms, Ammunition and Defense Articles. OMB No. 1140-0005(10/31/2019)"