It's not .22 caliber.
5.56mm is .224 inches
5.45 is .21? or there about. I've never slugged the bore of one.
That is where I would start.
Then see if anyone makes any high quality projectiles for it. I seriously doubt it.
The vast majority of ammo was created with a mild steel core and a bi-metal steel jacket for ease of mass production.
Just finding reloadable brass that is boxer primed and not berdan is going to be an issue.
Do your research before you drop your money into this one.
Most people form other cases into calibers that are common enough to get good/great accuracy out of it.
.223
6mm
6.5mm
7mm
.30
Are the one's you can find target grade projectiles for. These days you are going to have to wait to find any reloading components though.
There are a lot of interesting project rifles out there.
Personally I want a .22 Fireball.
I could do 99% of my hunting that I do with a .223 with it with only 75% of the powder volume.
However, I don't get out like I used to, and primers are almost unobtainable around here.
No money also.
All I can say is that there are a gazillion chamberings out there. Lots of folks have gone out and done darn near everything with any specific cartridge. If you do the appropriate research, I'm sure you can figure out what you need.