Casper

Many of the English made snap caps for the .410 bore do not have the calibre on. Some makers do not even head stamp the .410 size due to the small diameter. I have seen Westley Richards .410 snap caps without any calibre engraving so it is indeed possible they are .410.

It is however equally posisble that they are rifle snap caps also, (as many of these do not have calibre on either) and that they have the same as or near identical dimensions to a .410 cap

The only way to tell for sure is to try them out If they are for a rifle they will have a taper to reflect the NE case they correspond with, if they are largely parallel then the bet is they are .410.

Jonathan