I couldn't help but laugh when I followed your link.
These nipples, made for musket caps are,
manufactured from 12L14 steel and heat treated to just the right hardness.
:rotf:
12L14 steel is a low carbon steel that cannot be hardened with any heat treatment known to man.
Furthermore, low carbon steels are one of the worst things a nipple can be made from.
Because the steel can't be hardened, it will "mushroom" easily.
Because the steel doesn't contain any nickle or chromium it is subject to hot gas corrosion and wear each time it is used.
(The high temperature of the powder gasses will burn away the steel resulting in the small hole rapidly increasing in size.)
Good nipple material would be one of the hardenable stainless steels. An excellent nipple material would be one of the Inconels, a mixture of iron, cobalt and nickle.
(I've never seen a Inconel offered but it would make a dandy nipple. Jet engines use it in high temperature areas.
The main problem is, Inconel is expensive and it is tougher than owl poo to machine. It can rapidly wear down high speed cutters so carbide cutters are normally used to machine it.)
Several different bronze materials made by Ampco are hard and resistant to hot gas corrosion. Excellent nipples are made from these alloys, Tresco produced nipples made out of Ampco aluminum bronze.
Anyway, if your happy with them that's good. Just don't expect me to buy any.