Trays, not jars
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What a primer is
A small cup containing an impact-sensitive compound. Struck by a firing pin, it ignites and lights the propellant. Sensitivity is the function rather than a defect.
Which is why they ship in trays
Held separated, oriented the same way, and not able to strike each other. The packaging is part of the product rather than a shipping convenience.
A jar of loose primers is none of that
They touch, they are randomly oriented, and they move against each other every time the container is handled.
So this catalog does not offer a container for them
Not because a rule says so. Primers are explicitly named in the definition of ammunition and ammunition and its components are exempt from the federal explosives regulations.
Which is the same shape as the powder finding
The exemption describes the licensing scheme and says nothing about the material. The control is the packaging, and the right packaging came with the product.
Keep them in the tray and the sleeve
With the brand, type and lot visible. Primer types are not interchangeable and a load is developed around a specific one.
Large and small are two separate leaves here
Which reflects how a bench actually works: large rifle, small rifle, large pistol, small pistol and magnum variants are different components that look similar.
And mixing them is the quiet failure
A primer that seats and fires differently from the one the load was worked up with. The tray and the label are what prevent it.
Percussion caps are named separately in the rules
They appear in the black powder exemption alongside safety fuses and friction primers, which is a different list from the ammunition one.
Keep them away from the powder
Which is a bench layout point rather than a container one, and it is the single most repeated piece of advice in the craft. Separate storage, separate shelves.
And handle them as little as possible
Every transfer is an opportunity to drop, tip or compress a tray. A sleeve opened once and used from is handled less than one decanted into something else.
The advice is the same as for powder
Original packaging, original label, do not decant, and read the fire code that applies to you for quantities.