Hi guys, I'm new to this site and recently bought a used Handy rifle in .223 bull barrel. I searched for info on this gun and that brought me here

From some searching, it looks like my gun was made in 1996, ser. # NK26XXXX. My questions are,, where can I get a deer caliber barrel for it and will it require gunsmithing to install it? That 45/70 looks like fun or maybe just a 30/30 for my grandson! Also, what is the average cost for a different barrel?
Thanks in advance and this looks like a great site!!