Comment: They

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Jefferson's picture

They

are sold 2 different ways. 1 as you listed. The other as a "solvent trap adapter." It is to catch the cleaning solvents when you push a cleaning rod and brush from breech to muzzle when you are cleaning indoors so that you don't stain or ruin flooring. No stamp needed.
If someone got caught with a hole in the end of their "solvent trap" and it had powder residue in it, one could be looking at up to 10 years imprisonment and a several thousand dollar fine.

Definitely NOT a risk I would be willing to take.