The place to start is slugging your bore.
While you are at it,determine your twist rate.
I assume this is an old original rifle.
I would be cautious about using jacketed bullets.I do not know if the 405 WCF was originally loded with jacketed bullets,but a lot of the older barrels were made of very soft steel.Cast bullets are appropriate,and jackets may be hard on the rifling.I do not know that your rifle has a soft steel barrel,but I suggest finding out.
Hornady makes some nice brass.
After you know your bore dia,you can look to see what bullets are available,and work from there.
Hogdon sells a magazine format load manual.The last time I bought one it had.405 data.They used the Hornady jacketed .300 or 350 gr bullets,I forget which.As I recall,velocity approached 2400 fps.
But,understand,those are for some modern rifles,one being the 1895 Win remake.
The 10 mm bullets run .400.Your .405 will probably need at least .406 bullets,and more likely .410 to .413.
I'm sure more folks who know more than I do will help here,but this is fun!
