You're way off track.
The No. 12 nipples are made for original and reproduction Colt Walker and Dragoons, the big .44 revolvers that weigh four pounds or so, unloaded.
I think all reproduction Walker and Dragoons made today use No. 11 nipples but in the 1970s when these reproductions were introduced they used the No. 12 nipples, just like the originals.
The No. 12 has a slightly larger inside diameter than the No. 11. On the larger nipples it's a better fit than the No. 11.
I bought a couple tins of Remington No. 12s on a discount table in a sporting goods store years ago. I used caps from one tin for clearing the nipple in my .50-caliber muzzleloading rifle until I wised up.
I kept the other, sealed tin as a collectible.
I've heard that Remington has reintroduced the No. 12 cap but am uncertain about that. I can't imagine there's much demand for it.
And if your repro Walker or Dragoon requires No. 12 caps, then perhaps it's time to change its nipples to use the commonly available No. 11 caps.
If I were you, I'd offer them for sale on the internet. No. 12 caps are not easily found in my experience, someone might pay a good price for them.
