Gunsmith or maker.
H&R Handi-Rifle
50-165
1/10
50-200 USD or so
$200-$250, depending on condition.
The year is determined by the first letters not the numbers.
About $225, depending on condition, caliber, scope, etc.
No published sn data. You will have to call the factory.
Handi means activities done with the hand
The one issue with 5.56 in a handi rifle is the harder primers. You will almost absolutely have to install a heavier hammer spring. I have some Malaysian 5.56 and it often won't fire in the handi. I have heard the same about the Rossi single shots. As far as your concerns about pressures, the Handi handles all sorts of calibers on the same frame and barrel blank. Many of those push 65k or so. I don't worry about any difference in 223/556.
Gun is dirty- needs cleaning and lube. Parts worn, parts broken. Start with a proper cleaning and lube. If that does not fix the issue, have a gunsmith inspect parts. And it is a Handi-Rifle, not handy.
Well- sort of. Single shot top break rifles, such as the H&R Handi Rifle or the Thompson Center can change barrels, and can shoot several different cartridges- but not from one barrel.