I haven't made my own.
I see no reason to bother. There are several good products on the market so I use those.
Birchwood Casey Plum Brown is a heat activated browning solution. It requires the metal to be heated up to a temperature above 250 degrees F and below 290 degrees F to work right.
It also acts instantly but usually needs several coats to make the surface appear the same.
Because of this I have quit using it on large items like barrels but I do use it for small parts like lockplates/trigger guards (steel)/ butt plates (steel) and so forth.
The coating is very thin and easily scratched. If scratching isn't a problem it is quite resistant to normal wear.
Laurel Mountains browning agent is a cold process which needs fairly high humidity to work.
The rust it forms is very hard and difficult to scratch.
Although it takes longer to brown the part, IMO the final result is much better than the Birchwood Casey browning.