Maybe change it to:

"
4 Cartridges
Insert other side
"

Some engrave and emboss with Gold something boring on the barrel or collar. Something like:

"Bullet 400 grs, XX grs"

Like the user needs instructions what to load in their bolt action rifle. Maybe fine underneath out of sight. For what the open sights have been set up for. Plus velocity. Especially for a Double Rifle, what the rifle barrels were regulated for. But out of sight. But maybe the usual customer would never see it there, taking their bespoke rifle to the gunsmith for "servicing". Tally ho, old chap.

"Point this end at target", would be good at the muzzle.

"Pull this", on the trigger.

:O