Following WWI, Krag rifles were sold off by the government for $1.50 each. Many, many of them were purchased and modified as your has been. There are still many of them out there on the used market. I have two such modified Krags. Yours looks like an excellent example. The front sight band and sight are from a 1903 Springfield. Your rifle has been reblued at some point in it's life.
I killed my first deer with such a modified Krag in 1960 and I still have the rifle. I paid the huge sum of $15.00 for it from an old Dentist who had given up hunting. For grins below is a pic.
The only cast bullets tip I can give you is these rifles have large throat and give their best cast bullet accuracy with long heavy 200 grain plus cast bullets sized .312 - .313.
Best of luck with this fine old family heirloom.